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TH E 



OF 

ENERGY. 


A MANUAL FOR THE DESIGN OF ELECTRICAL CIRCUITS. 


BY ^ 

ARTHUR VAUGHAN ABBOTT, C.E., 

f. 

CHIEF ENGINEER CHICAGO TELEPHONE CO., MEMBER AMERICAN INSTITUTE OF ELECTRICAL 
ENGINEERS, MEMBER AMERICAN INSTITUTE OF MINING ENGINEERS, 

JUNIOR AMERICAN SOCIETY OF CIVIL ENGINEERS. 


WITH NINE FOLDING PLA TES. 



NEW YORK: 

D. VAN NOSTRAND COMPANY. 

LONDON: 

SAMPSON LOW, MARSTON & COMPANY, Limited. 

1898. 
























Entered according to Act of Congress in the year 1898, by 
Arthur V. Abbott, 

In the office of the Librarian of Congress at Washington, 

Y / > pi :c j.t p - .*rn 

fl*VlUyw» ..O A'-wctii 




TYPOGRAPHY BY C. J. PETERS & SON, BOSTON. 


PRESSWORK BY J. L. BLACK, NEW YORK. 






PREFACE. 


It has been tritely remarked that “ There is nothing new under 
the sun.” In view of this sapient aphorism the reader will not ex¬ 
pect to find much that is strange or remarkable in the present vol¬ 
ume. Books, however, are something like kaleidoscopes, in which 
ideas, like the bits of colored glass, resolve themselves into innumer¬ 
able stellate forms, presenting to the inspector picture after picture, 
each of seemingly different origin from the preceding ones. While 
investigating a subject, it has been the custom of the author to obtain 
all the works by different writers on the question under consideration, 
and to read them successively ; thereby viewing the matter from a 
number of different standpoints. He has found this an exceedingly 
valuable way of acquiring information, and remembers with the live¬ 
liest sense of gratitude the various expositors from whose differing 
horizons he has scanned the landscape of complicated topics. 

The present volume has been prepared chiefly from the aspect of 
the author’s experience, and is an endeavor to collect and arrange in 
an accessible and convenient form the data necessary to the scien¬ 
tific designing and proportioning of Electrical Circuits. No attempt 
has been made to describe any Central Station machinery ; for the 
scope of the volume would not permit of an extension beyond the 
material relevant to the “Transmission of Energy,” so aptly and 
untranslatably termed by the French “ Canalisation .” 

The opening chapters are devoted to an outline of Circuits, and 
to an annunciation of the principles and laws governing Conductors 
and Insulators. This is followed by a discussion of the methods of 
constructing Aerial Lines and description of Underground Conduits 


m 



IV 


PREFACE. 


and Conductors. Succeeding these, a chapter is devoted to Testing 
Instruments, and one to the Methods of Measuring and Inspecting 
Lines, and of determining and remedying any faults that may be found 
to exist. In Chapters VII. and VIII., the laws of Continuous and 
Alternating Circuits are exhibited. Subsequently, distribution proper 
is treated in three chapters, under the heads of “ Series Distribu¬ 
tion,” “Parallel Distribution,” and “Miscellaneous Methods.” In 
the concluding chapter, a rough approximation is given for obtaining 
the cost of Circuits and cost of the production of Electrical Energy. 

It has been the attempt of the author to herein collate such 
methods of Circuit Construction, in connection with tabulated data, 
as have been sanctioned by the best practice, both in this country 
and in Europe. No attempt has been made to render the volume an 
encyclopedia; and, therefore, all matter obsolete or antiquated has 
been rejected, and only such is presented as seems to be fully war¬ 
ranted by the present state of the art. Wherever possible, the lines 
along which future practice is likely to lie have been indicated. The 
chapters on measuring instruments and methods of testing have 
been carefully abridged to include only such information as is valu¬ 
able to the practicing engineer, laboratory appurtenances and meth¬ 
ods being entirely eliminated. In a large proportion of the methods 
of measurement, the simple literal formulae for the solution of the 
problem in question are given, without any attempt at the necessary 
demonstration of the truth of the same. Inasmuch, however, as 
nearly all such formulae are directly derivable from the laws of Ohm 
and Kirchhoff, involving only algebraic processes, the reader can 
easily deduce the equations for himself. For a more complete expo¬ 
sition of the methods of measurement, the reader is referred to the 
works of Hospitalier, Gerard, Weiller & Vivarez, Kempe, and Monroe 
& Jameson. In the chapters on Distribution, sufficient importance is 
attached to the subject to give the mathematical discussion in full, 
involving, however, only the simplest applications of the calculus. 
Wherever practicable, liberal use of illustrations has been made ; for 


PREFACE. 


V 


ocular demonstration is always much clearer and more concise than 
any verbal description. 

To the works of Picou, Hospitalier, Cadiat, Gerard & Weiller, 
Kempe, Thomson, Kennedy, Ayrton, Perry, Preece, and Heaviside, 
and to the “Transactions of the Electrical Engineers,” th z London 
Electrician, the Electrical World, the Electrical Engineer, and La Lu- 
milre Electriqnc, also the Street Railway Journal, the author has 
long been indebted for information that has happily led to the suc¬ 
cessful construction of many transmission plants, and which, passed 
through the sieve of experience, is here presented to the public; and 
for benefits thus derived, he has long wished for an opportunity to 
gratefully acknowledge his obligation. Acknowledgment is particu¬ 
larly due to Mr. F. J. Dommerque, for aid in the preparation of 
many of the tables, and in verification of the proof-sheets. Con¬ 
vinced, from the standpoint of experience, of the utility of the infor¬ 
mation, the author trusts that the electrical section of the engineering 

\ 

profession may find the present presentation of value in practical 
construction. 

Chicago, III., Jan. 15, 1895. 



PREFACE TO SECOND EDITION. 


In the three years which have elapsed since the publication of 
the first edition of The Electrical Transmission of Energy , the ex¬ 
tension of practical applications of electricity has even far exceeded 
the most sanguine prophesies of growth ; but during this time prog¬ 
ress has been chiefly along commercial lines rather than those of 
invention. Few new or startling ideas may be chronicled, but, 
through the furnace of practical experience, that which was good 
has been refined and freed from the dross of theory, — has settled 
into secure and reliable commercial forms. The Author, there¬ 
fore, has little to add or change in such portions of this work as 
are purely theoretical, but details of practice have received careful 
revision. 

It was with much apprehension that the Author watched the 
reception of the first edition, but its appearance developed so many 
hitherto unknown friends, and even its most severe critics were 
withal so just and kindly, that a feeling of gratitude soon displaced 
fear; and to all who have aided, either with welcome words of 
commendation, or the more valuable though perhaps less pleasing 
phrases of criticism, the Author here returns his most sincere 
acknowledgments. 

Chicago, Nov. i, 1898. 


vi 











TABLE OF CONTENTS. 


CHAPTER I. 

Introduction.. 1 

Distribution in General. — Distribution in Series.— Distribution in Parallel. — Mixed 
Systems.— Indirect Distribution. 


CHAPTER II. 

The Properties of Wire. 4 

The Conducting Circuit.— Wire Manufacture. — Hard Drawing. — Wire Gauges.— The 
Circular Mil. — Copper W'ire.—Properties of Wire. — Composite Wire. — Galvanizing and 
Tinning. — Insulated Wire. — Flexible Cable. — Testing and Inspection. — Wire Specifica¬ 
tions.— Tension of Aerial Lines. — The Influence of the Variation of Temperature. 

CHAPTER III. 

The Construction of Aerial Circuits.36 

PART I.— GENERAL LINE WORK. 

Classification.— Aerial Lines. — Poles. — Methods of Preservation.— Height of Poles. — 
Cross-Arms. — Pins. — Facing of Arms. — Stresses. — Calculation for Pole Strength. — Guy¬ 
ing. — Anchor Poles. — Setting Poles. — Insulators. — Value of Insulators. — Oil Insulators. — 
Tying and Dead-Ending. — Loops. — Stringing Wires. — Wire Joints. — Strength of Joints. — 
The Suspension of Aerial Cables.— Humming of Wires.— Transposition of Telephone Lines. 

— Power Circuits.— Pole-Line Specifications. 

PART II. —ELECTRIC RAILWAY CIRCUITS. 

Electric Railway Circuits. — Railway Return Circuit. — Electrolytic Action.— Railway 
Poles. — Wooden Poles. — Iron Poles. — Feed Wire Insulators and Pole Tops.— Trolley In¬ 
sulators. — Railway Line Work. — Strain Insulators. — Anchors. — Line Sections. — Switches. 

— Line Crossings. 

PART III —LIGHTNING ARRESTERS. 

Lightning Guards and Strong Current Arresters.— High Resistance Arrester. — Mag¬ 
netic Blow-out Arrester. — Mechanical Magnet Arrester. — Air Expansion Arrester. — Non-arcing 
Metal Arrester.— Discriminating Arresters. — Automatic Cut-outs.—Cable and Switchboard 
Protectors. — Appendix of Insurance Regulations. 


CHAPTER IV. 

Construction of Underground Circuits.141 

PART I —CONDUITS. 

Classification. — Valentine Conduit. — Wyckoff Conduit. — Paper Conduit. — Pipe Con¬ 
duits._Dorset Conduit. —Chenowith Conduit. — Terra-Cotta Conduits. — Crompton System. 

— Brooks System. — Johnstone System. — Kennedy System. — St. James System. — Inflexible 







TABLE OF CONTENTS. 


Ylll 


Systems. — Callender Solid System. — Cologne Conduit. — Zurich Conduit. — Manholes.— 
Junction Boxes for Street Railway Feeds. — Introduction of Circuits.— Pneumatic Rodding. 

— Gas.— Electric Railway Conduits.— Buda-Pesth Conduit. — Blackpool Conduit. — Love 
Conduit. — Lenox Avenue Conduit. — Metallic Conduits for Alternating Currents. 

PART II. —CABLES AND CONDUIT CONDUCTORS. 

Conduit Conductors. — Armored Cables.— The Siemens Cable. — The Edison System. 

— The Ferranti Mains. — Telegraph Cables. — Subaqueous Cables. — Power Circuits. — Paper 
Cables.— Telephone Cables.— British Post-Office Cables.— The Patterson Cable. — Glover 
Cables. —Fowler-Waring Cables.— Felten-Guilleaume Cable.— Beaded Cables. — Cable Joints. 

— The Connection of Underground and Aerial Systems. — Cable Heads. 


CHAPTER V. 

Electrical Instruments.198 

Classification. — Instruments for Measurement of Resistance. — Wheatstone Bridge.— 
Slide Wire Bridge. — Ohm-meter. — Instruments for Measuring Quantity and Pressure. — D’Ar- 
sonval Galvanometer. — Ballistic Galvanometer. — Galvanometer Constants.— Reduction to 
Zero and Inferred Zero. — Shunts. — Weston Instruments. — Cardew Voltmeter.— Electrostatic 
Voltmeter. — Siemens Dynamometer. — Condensers. — Wattmeters. — Keys. — Magneto. — 
Ground Indicators.— Boyer Speed Recorder. 


CHAPTER VI. 

Methods of Electrical Measurement.223 

Quantities to be measured. — Electrical Intensity. — Electrical Quantity. — Unit of Cur¬ 
rent. — The Watt. — Capacity. — Resistance. — Ohm’s Law. — Kirchhoff’s Laws. — Measure¬ 
ment of Resistance by Deflection. — By Wheatstone Bridge.— By Voltmeter.— By Volt and 
Ammeter. — Measurement of Small Resistance. — High Resistance. — Insulation Resistance. 

— By Loss of Charge. — Line Resistance. — Ground Resistance. — Special Methods for Galva¬ 
nometer Resistance. — For Battery Resistance. — Potential Difference.— By Condenser.— 
Wheatstone’s Method. — Lumsden’s Method. — Measurement of Current Strength by Amme¬ 
ter. — By Voltmeter. — By Differential Galvanometer. — By Slide Wire. — Measurement of 
Capacity. — Thomson’s Method. — Gott’s Method. — Divided Charge Method. — Localization 
of Faults. — Blavier’s Method. — Overlap Method. — Loop Test. — Murray’s and Varley’s 
Methods. — Localization of Crosses.— Measurement of Inductance.— By Condenser and Bridge. 

— With Alternating Current.— Mutual Inductance.— Measurement on Alternating Currents. 

— Difference of Potential. — Current.— Power by two Voltmeters. — By three Ammeters.— 
Measurement on Polyphase Circuits. — Electrical Railway Testing. — Capacity of Aerial 
Lines. — The Inductance of Aerial Lines.— Mutual Inductance on Transmission Lines. 


CHAPTER VII. 

Continuous Current Conductors.2(58 

PART I.—CONDUCTORS AND INSULATORS. 

Conductors. — Resistance. — Ohm’s Law. — Specific Resistance. — Effect of Temperature. 

— Resistance of Dielectrics. — Line Leakage. — Distribution of Potential. — The Effect of 
Leakage. — Conductance. — Distribution of Potential in Branch Circuits. 

PART II —THE HEATING OF CONDUCTORS. 

Joule’s Law. — Location of Circuits. — Bare Wires Freely Suspended.— Radiation and 
Convection. — Paneled Wire. — Insulated Wire Freely Suspended.— Rheostats and Heaters. 

— Cost of Electric Heating.— Fuse Wires.— Heating of Insulated Cables.— Heating of Con¬ 
duit Cables. — Heating of Suspended Cables. 





TABLE OF CONTENTS. 


IX 


CHAPTER VIII. 

Conductors for Alternating Currents.811 

General Considerations. — Classification. — Skin Effect. — Current Density. — Inductance. 

— Magnetic Field. — Electro-motive Force due to Varying Field.— Equation of Energy.— 
Harmonic Motion. — Average Values. — The Solution of the Energy Equation.— Effect of 
Mutual Inductance. — General Energy Equation for Mutually Inductive Circuits.— Coefficients 
of Inductance.— Effect of Capacity. —Solution of the Energy Equation for Circuits with Ca¬ 
pacity. — The Energy Equation for Circuits containing Resistance, Inductance, and Capacity. 

— Graphical Methods. — Vector Quantities. — Composition and Resolution of E.M.F .— 
Simple Circuits with one Resistance and Inductance in Series. — Reactance. — Impedance. 

— Resistance Variable. — Inductance Variable. — Simple Circuits with Several Resistances 
and Inductances in Series. — Simple Circuits with one Resistance and Capacity in Series. — 
Simple Circuits with Several Resistances, Inductances, and Capacities in Series. — Circuits 
with Resistance, Inductance, and Capacity in Parallel.— Method of Equivalent Resistance 
and Inductance. — Circuits containing Mutual Inductance. — Impedance Tables. 


CHAPTER IX. 

Series Distribution.372 

Origin. — Classification. — Constant Current Circuits with Generator and Motor at Fixed 
Distances. — Location of Station. — Current Density in Main Circuit. — Economic Conditions. 
— Design for Heating-Limit.— Design for Mechanical Strength. — Minimum First Cost of 
Line. — Minimum First Cost of Station. — Minimum First Cost of Plant, and Minimum Cost 
of Maintenance and Operation. — Design for Minimum First Cost of Plant.— Design for Best 
Service. — Minimum Cost of Plant for Maximum Income.— Calculation of Loads. — Regula¬ 
tion.— Automatic Cut-outs. 


CHAPTER X. 

Parallel Distribution.402 

The Evolution of the Parallel System. — Methods of Distribution. — The Loop System. 

— The Spiral Loop. — The Tree System.— The Closet System. — Conical Conductors.— 
Anti-Parallel Feeding. — Distribution of Potential. — Cylindrical Conductors, Parallel Feed¬ 
ing.— Cylindrical Conductors, Anti-Parallel Feeding. — Conical Conductors, Parallel Feeding. 

— Conical Conductors, Anti-Parallel Feeding. — Three-Wire System. — Multiple-Series Sys¬ 
tem.— Five-Wire System. — Relative Area covered by the Multiple-Wire Systems. — Feeder and 
Main System. — Location of Central Station.— Location of the Feeders and Centers of Dis¬ 
tribution.— Distributing-Mains. — Calculation of Feeders. — Efficiency of Conductors.— 
Methods of Regulation. — The Compensator. — The Compensator in Electrical Railway Work. 

— Fall of Pressure and Necessary Section for Feeders. — Laws of Economy and Feeder Design. 

— General Design for a System in Multiple Arc. — Mechanical Methods. — Station Loads.— 
Arc Lamps on Constant Potential Circuits. — Electric Railway Wiring.— Three-Wire Rail¬ 
way Systems. 


CHAPTER XI. 

Miscellaneous Methods and Long-Distance Transmission.488 

Motor Transformers.—Compensators. — Motor Transformers Running and Feeding in 
Series.— High and Low Potential Distribution from the same Station.—Accumulators.— 
Sub-Station Accumulators. — Accumulator Distribution.— Regulation by means of Accumula¬ 
tors.— Transformers. — Economy in Conductors. — Isolated Transformers.— Efficiency of 
Distribution by Isolated Transformers. — Transformers as Sub-Stations. — Polyphase Systems. 





X 


TABLE OF CONTENTS. 


— Long-Distance Plants. — Long-Distance Transmission with Continuous Currents. — Line 
Construction for Long-Distance Transmission. — Relative Amount of Conducting Material for 
Transmission Systems. 


CHAPTER XII. 

The Cost of Production and Distribution.528 

Cost of Conductors. — Cost of Conduits. — Telephone and Telegraph Lines.— Railway 
Lines. — Cost of Power-Stations. — Cost of Producing Energy. — Coal Consumption per Watt 
Hour. — Water-Power. — The Gas-Engine.— The Cost of Electrical Energy, as developed by 
Wind-Power. — The Actual Cost of Electrical Energy. — Commercial Considerations of Trans¬ 
mission Problems. 



TABLE OF SYMBOLS. 


A.Ammeter, amperes. 

a .Coefficient in temperature equation for dielectric. 

a .Coefficient in temperature equation, also angular measure. 

a , 3 , d , and x . . Resistances in the arms of a Wheatstone Bridge. 

/3 .Coefficient in temperature equation, also angular measure. 

C .Condenser or capacity, and radiation coefficient. 

D, d, d', d ", etc. Deflection on any scale instrument, or diameter. 

d c .Rate of depreciation charged on cost of conduits. 

di .Rate of depreciation charged on cost of line. 

d s .Rate of depreciation charged on cost of station. 

E .Primary electro-motive force or battery. 

e .Electro-motive force at any secondary point. 

F .Number of hours per annum of operation; also galvanometer figure 

of merit. 

G .Galvanometer and galvanometer resistance. 

g and g' .The two halves of a differential galvanometer. 

H .Heat units (gramme, degree). 

H c .Heat units lost by convection. 

H r .Heat units lost by radiation. 

/, /', I" .(and?, i', i", etc.) Currents in amperes, also rate of interest. 

K and k .Key and coefficient of radiation per unit of surface. 

K .Cost of producing energy per watt or K. IV. 

K' .Cost of station machinery per watt or K. IV. of output. 

L and /.Length. 

m .Multiplying power of shunt. 

Q .Quantity of electricity in coulombs. 

R, R ', R" .... Resistance unknown. 

r, r\ r" .Resistance known. 

Rt .. . Resistance at temperature /°C. 

R 0 .Resistance at temperature 0 ° C. 

p .Resistance specific. 

S .Shunt, area of cross-section, and crushing strength. 

T .Time in seconds, also temperature, tension in pounds. 

t .Conductor temperature in degrees C. 

0 .Temperature of air in degrees C. 

U' .Charge for interest and depreciation on line. 

U" .Energy lost in transmission in line. 

u 0 — u' .Drop on line. 

V .Voltmeter and voltage. 

xi 





































• ^ # • • . • J • *- f • ••• 


Xll 


TABLE OF SYMBOLS. 


mV . 

PV and 7 a ... . 

PV C . 

W r . 


Milli-meter voltmeter. 

Energy in watts. 

Energy in watts lost by convection. 

Energy in watts lost by radiation. 

Annual cost to produce IV watts. 

Deflection. 

Electro-motive force at any given instant. 

Current at the same instant. 

Number of magnetic lines cut, or in field at any given instant 
VThe maximum values of the above quantities. 


Z/, etc 


M.F. 
c.m. . 
s.m. . , 
2 • • 


I The mean value of the above quantities. 

Coefficients of inductance. 

Coefficients of mutual inductance. 

Time of one complete period. 

Amplitude of harmonic motion. 

Angle of epoch. 

Angle described in time t or dt. 

The frequency or number of periods per second. 

2 7 Til. 

Strength of a magnetic pole. 

Distance. 

The total induction, or induction per unit of area. 
Magnetizing force. 

Impedance. 

> 

Impedance Factor. 

Electro-motive force. 

Circular mils. 

Square mils. 

Sign for summation. 


When the symbols are applied to different circuits sub-letters are used to denote it 
corresponding value for each circuit. 


































LIST OF TABLES. 


Page. 

Table of Symbols.xi, xii 

Chap. Table. Title 

II. 1 Physical Properties of Iron and Steel Wire. 5 

2 Comparison of Wire Gauges. 7 

3 Variation in the Resistance of Copper due to Varying Purity ... 9 

4 Properties of Copper Wire.11 

5 Safe Currents for Paneled Wire.12 

6 Fall of Potential in Copper Wire.12 

7 A Properties of Silicon Bronze Wire.14 

7 B Properties of Silicon Bronze Wire.16 

8 Approximate Weights per Mile of Insulated Wire.19 

9 Stranded Cables.23 

10 Circular Millage of §, §, fa, 1, 2, and 3 Wire.24 

11 Data of British P.O. Wire (Copper) Specifications.26 

12 Data of British P.O. Wire (Iron) Specifications.28 

13 Sags and Tensions for Aerial Lines t .34 

III. 14 Tensile Strength of Timber.43 

15 Crushing Strength of Timber.43 

16 Dimensions of Anchor Poles.53 

VII. 17 Resistance of Metals.270 

18 Resistance per Grain-foot and Mil-foot.271 

19 Value of a and [i in Formula Rt = R 0 (1 -+- at -j- ^/ 2 ).272 

20 Value of a in Formula Rt = R 0 (1 + oil) .272 

21 Specific Resistance of Insulators.275 

22 Relative Conductivity of Copper.291 

23 Values of .00175 + .013^, n (.05625) (1.0077) and 1.007* — 1 292 

24 Current Curves for Aerial Wires. Pocket. 

25 Current Curves for Wire in Still Air.293 

26 Safe Currents for Paneled Wires.294 

27 Rise in Temperature for Paneled Wires.296 

28 Safe Current for Galvanized Iron Wire. Rheostats.297 

29 Safe Current for Tinned Iron Wire. Rheostats.298 

30 Safe Current for German Silver Wire. Rheostats.299 

31 Constants for Fuse Wires.299 

32 Fuse Wires by Preece.300 

33 Commercial Fuse Wires.300 

34 Lead and Tin-foil Fuses.301 

35 Lead and Alloy.302 

36 Relation between Length and Carrying Capacity.303 

37 Effect on Carrying Capacity of Fuse Wires of the Duration of Current 304 

xiii 






































38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55 

5G 

57 

58 

59 

60 

61 

62 

63 

64 

65 

66 

67 

68 

69 

70 

71 

72 

73 

74 

64 

75 

76 

77 

78 


LIST OF TABLES . 


Title. Page. 

Carrying Capacity of Lead and Tin Fuse Wires.. . 305 

Fuse Wire Curves, Lead and Tin Alloys.30& 

Specific Thermal Conductivity.308 

Temperature Relations of U. G. Cables.309 

Thickness of Shell on Cylindrical Conductors Affected by the Current 

in an Alternating Circuit.314 

Factor for Virtual Resistance.315 

Impedance Tables. Pocket 

Multipliers to Transform E.S.C.G.S. Units into M.F. per Unit of 

Length.368 

Specific Inductive Capacity.371 

Section A. — Cost of Laying One Additional Ton of Copper . . . 390 

B. — Sectional Area for 100 Amperes.391 

Hours of Lighting. 395 

Hours of Lighting.395 

Hours of Lighting ..395 

Relation between Cases I., II., III., and IV.422 

Areas Covered by Multiple Wire System.435 

Calculations for Point of Least Pressure.466 

Heating-Limit for Conductors — 

Sheet I. Buried Conductors. 472 

Sheet II. Aerial and Paneled Conductors.473 

Sheet III. Minimum Safe Diameter of Copper Wire .... 474 

Relative Amounts of Conducting Material in Various Conducting 

Systems. 528-533 

Cost of Conductors.528 

Cost of Conduits. 534-536 and Pocket 

Cost of Pole Lines.537 

Cost of Street Railway Lines.538 

Estimate of Overhead Lines.539 

Operating Expenses of Street Railways.538 

Cost of Power Stations.540 

Cost of Electrical Energy per K.W.541 

Watt Hours per Lb. of Coal.542 

Possible Watt Hours per Lb. of Coal.543 

Cubic Feet of Gas per B.H.P.544 

Cost of Electrical Lighting by Wind-Power.545 

Cost of Producing Energy.546 

Cost of Producing Energy.547 

Cost of Production in Continental Stations.548 

Comparison of Operating Expenses ..550 

Cost and Operating Expenses of Lighting Station.551 

Cost of Plant and Operating for Arc Light Stations.552 

Cost of Installing and Maintaining Steam Plants. 556-559 

Sheet A. Pocket. 

Cost of Energy per H.P. per annum. Pocket 

Tables for determining Economical Conductor Sections . . . Pocket 

Tables for determining Economical Conductor Sections . . . Pocket 

Tables for determining Economical Conductor Sections . . . Pocket 









































THE 


Electrical Transmission of Energy. 


CHAPTER I. 

INTRODUCTION. 

ELECTRICAL DISTRIBUTION. 

Art. 1. Distribution in General. — The distribution of Elec¬ 
tricity comprises a study of the appropriate methods for supplying 
Electrical Energy, generated by one or more sources, to a number of 
receiving mechanisms, or translating devices, the quantity given 
to each one being properly proportioned to its needs; the investiga¬ 
tion of the conditions for accomplishing this distribution in the most 
exact and economical manner; and finally an examination of the 
means whereby distributing plants may be rendered permanent, 
durable, and secure. 

The methods of distribution are chiefly controlled by the way in 
which it is considered advisable to arrange the receiving mechanisms. 
This arrangement of the receivers is indicated by the service which 
they are called upon to perform, and being involved in the design of 
the plant in question, must be settled in each particular case for 
itself. 

Three principal methods are common for the arrangement of the 
receiving mechanisms ; they may be arranged in Scries , in Parallel , 
or by a Combination of the two previous methods. It is also fre¬ 
quently advisable to employ, between the generators and the re¬ 
ceivers, intermediate or auxiliary contrivances, such as accumulators, 
transformers, or the like, the use of which gives rise to the various 
problems in indirect distribution. 

1 



2 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


in Series. — Under this method all of the 
one after the other in 




Fig. i. 


Diagram of a simple 
Series Circuit. 


2. Distribution 

receivers are placed 

succession upon a single conductor extending 
throughout the entire circuit from pole to 
pole of the generator. This method is illus¬ 
trated in Fig. 1. 

3. Distribution in Parallel. — In this 

system one or more 
pairs of conductors, 
running parallel to 

each other, are arranged, extending to the 
limits of the circuit. Each receiver is con¬ 
nected across one of the pairs of mains, 
thus forming a circuit which is independent 
of that of every other receiver. See Fig. 2. 

4. Mixed Systems. — A combination 
of the two preceding methods is a natural 
consequence, giving rise to designs as ex¬ 
emplified in Fig. 3, some of the receivers 
being placed in parallel, as previously indi¬ 
cated, while others may be placed in series 
and joined across the mains from the gener¬ 
ator, each series circuit being arranged in 
parallel to all the other series circuits, thus uniting in one both 


Fig. 2. Diagram of a simple 
Parallel Circuit. 



systems. Obviously, to unite the generators in series and then to 
place them across the mains in parallel, in a manner similar to the 
arrangement of the receivers, readily followed ; giving rise to the now 












































IN TROD UC TION. 


3 



famous three, five, and seven wire systems now used for direct 
current distributions of magnitude. 

5. Indirect Distribution. — Finally, if between the generator 
and the receiver intermediate contrivances for transformation or accu¬ 
mulation of Electrical Energy are em¬ 
ployed, the arrangement of the circuits 
between the generator and the accumu¬ 
lator, or transformers, and between the 
latter and the receivers, may be entirely 
different. For example, Fig. 4 shows 
in outline the combination of a lamp 
circuit fed by accumulators charged 
from a generator; the accumulators 
are in series across the mains of the 
generator, while the lamps are placed 
in parallel across two halves of the battery of accumulators. 

The various methods here outlined, together with the ramifications 
and modifications practically found to be of advantage, will be suc¬ 
cessively considered, proceeding from the simple to the more com¬ 
plicated forms. Previously, however, it is advisable to examine the 
characteristics of the materials adapted to the construction of electric 
circuits ; and to study such methods of construction as the present 
state of the art indicates as advisable. It is also desirable to become 
sufficiently familiar with electrical instruments and methods of meas¬ 
uring to enable the practitioner to examine into and determine the 
performance of a transmission plant, and to remedy any defects or 
faults that may be revealed. 


Fig. 4. Diagram of Indirect Distribution. 
























4 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


CHAPTER II. 

THE PROPERTIES OF WIRE. 

Art. 6. Every present system for the distribution of energy 
by electricity comprises, as its most important constituent, a circuit 
formed of some substance which is a good conductor of electricity, 
and which, connecting the generators and various receivers, conveys 
to each its appropriate supply. Inasmuch as the metals are the best 
conductors, they are universally selected to form at least a part of 
the conducting circuit, and for this purpose are most conveniently 
employed in the form of bands, or rods of small dimensions usually 
termed wire. 

7. Wire Manufacture. — While a detailed description of the 
process of wire manufacture is foreign to the scope of this work, 
it is advisable to outline it sufficiently to enable a proper design for 
the line circuit to be made. So far as the distribution of electrical 
energy is concerned, but three kinds of wire have any commercial im¬ 
portance, — iron wire, copper wire, and the various forms of bronze. 
The metal to be formed into wire is cast, or rolled, into masses about 
six inches square by three or four feet in length, technically termed 
“ Blooms ; ” and each bloom is then, by succeeding passes through 
rolls, reduced to a long and slender rod about half an inch in diam¬ 
eter, and approximately of a circular section. Wire smaller than 
this size it has been found impracticable to roll. For the lesser 
diameters recourse is had to the process of wire drawing, which 
consists in pulling the rolled rod through constantly decreasing holes 
in a series of hardened steel or agate plates. Thus the rod is given 
an exact circular cross-section, and by repeated passes through the 
dies may be reduced in diameter to any desired extent. 

8. Hard-Drawing. — Pulling the metal through the die produces 
a change in its molecular structure, whereby the rod becomes consid¬ 
erably compressed and hardened, its tensile strength being markedly 
augmented, with a corresponding diminution in elasticity. This 
effect, which seems to be analogous to the process of tempering in 



THE PROPERTIES OF WIRE. 


5 


steel, becomes of great importance in increasing the strength of the 
material forming the wire. Steel having a tensile strength of 60,000 
lbs. to 80,000 lbs. per square inch in the bloom, may by this so-called 
method of “hard-drawing” have its tenacity raised to 800,000 or 
350,000 lbs. per square inch. This extraordinary increase is, how¬ 
ever, only found in wire of very small diameter. The effect of hard- 

Table No. 1. 

Physical Properties of Iron and Steel Wire. 


Wire 

Gauge 

No. 

I. SAV.G. 

Diam¬ 

eter 

IN 

Mils. 

Weight 

per 

Mile, 

Lbs. 

Breaking Stress in 

Lbs. for Iron. 

Breaking Stress in 

Lbs. for Steel. 

Resis¬ 

tance 

per Mile, 

Ohms. 

Bright. 

Annealed. 

Bright. 

Annealed. 

7-0 

500 

3404 

15,700 

10,470 

20,310 

13,611 

1.435 

6-0 

464 

2930 

13,525 

9,017 

17,583 

11,722 

1.666 

5-0 

432 

2541 

11,725 

7,814 

15,243 

10,159 

1.921 

4-0 

400 

2179 

10,052 

6,702 

13,067 

8,712 

2.241 

3-0 

372 

1885 

8,694 

5,796 

11,302 

7,534 

2.590 

2-0 

348 

1649 

7,608 

5,072 

9,891 

6,593 

2.961 

1-0 

324 

1429 

6,595 

4,397 

8,573 

5,726 

3.420 

1 

300 

1225 

5,655 

3,770 

3, 1 51 

4,901 

4.000 

2 

' 276 

1037 

4,785 

3,190 

6,221 

4,147 

4.720 

3 

252 

864 

3,990 

2,660 

5,187 

3,458 

5.653 

4 

232 

732 

3,381 

2,254 

4,395 

2,930 

6.670 

5 

212 

612 

2,824 

1,883 

3,672 

2,447 

7.980 

6 

192 

502 

2,316 

1,544 

3,011 

2,007 

9.730 

7 

176 

422 

1,946 

1,298 

2,530 

1,668 

11.60 

8 

160 

348 

1,608 

1,072 

2,091 

1,393 

14.05 

9 

144 

282 

1,303 

869 

1,694 

1,130 

17.31 

10 

128 

223 

1,030 

687 

1,339 

893 

21.8 

11 

116 

183 

845 

564 

1,099 

734 

26.7 

12 

104 

148 

680 

454 

884 

590 

33.00 

13 

092 

114 

532 

355 

691 

461 

42.7 

14 

080 

88 

402 

268 

523 

349 

55.5 

15 

072 

70 

326 

218 

424 

284 

69.8 

16 

064 

56 

257 

172 

334 

223 

86.2 

17 

056 

42 

197 

131 

256 

170 

116.2 

18 

048 

32 

145 

97 

188 

128 

152.16 

19 

040 

21 

100 

67 

130 

87 

232.5 

20 

036 

18 

82 

55 

106 

72 

261.5 


drawing seems to be chiefly confined to a very thin layer or skin on 
the surface of the wire ; so if any mechanical abrasion occurs to the 
surface, such as cutting or nicking, sufficient to destroy the integrity 
of this skin, the entire effect of the drawing will be lost. For this 
reason great care must be exercised in the erection of hard-drawn 
wire to prevent this destruction of the exterior. The same effect 
may be produced by annealing. In Table No. 1 the physical charac- 




















6 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


teristics of hard-drawn and annealed iron and steel wire of the more 
common sizes are given. Unfortunately the process of hard-drawing 
reduces the electrical conductivity of copper wire from 2 to 4 per 
cent; yet the advantages to be derived from increased tenacity more 
than counterbalance this loss. Attempts have been made to man¬ 
ufacture all but the smallest sizes of wire entirely by rolling ; and 
while the results thus far obtained point toward a very successful 
accomplishment of this process, rolled wire is not as yet of common 
commercial occurrence. Curiously, in wire thus manufactured, the 
hardening of the metals by the rolls seems to extend entirely through 
the wire, and not to be confined to a superficial skin. In order to 
make good wire, it is necessary that the blooms from which the rods 
are rolled should be sound, and free from all slivers, gas bubbles, 
cold shuts, or other imperfections ; for, during the passage of the 
metal through the rolls and dies, all flaws in the blooms are simply 
elongated without being eradicated, tending to make the finished 
wire imperfect and difficult for the linemen to handle, as slivers or 
checks on the surface of the wire are likely to severely cut or injure 
the hands of the workmen, and make the process of stringing not 
only disagreeable but positively dangerous. 

9. Wire Gauges. — Until recently an enormous amount of con¬ 
fusion existed as to the terminology applied to the different sizes of 
wire ; and, indeed, in many instances the same trade name was applied 
by different manufacturers to wire of widely varying diameters. 
Even in 1883 a number of different wire gauges existed in Europe, 
and at least three different standards were in vogue in this country. 
The mistakes arising from the confusion of the gauges became so 
important that the iron and steel manufacturers met with a view of 
discussing this question, and of settling upon some universal stan¬ 
dard to be adopted by all of the trade. Joint meetings of the Iron 
and Steel Institute of Great Britain, and of the American Institute 
of Mining Engineers, resulted in the establishment in England of 
the Imperial Standard Wire Gauge, and of the .adoption in this 
country of the Brown & Sharp Gauge. On the Continent gauge 
numbers are rarely used, all wire work being measured in millimeters 
and decimal fractions thereof. In Table No. 2 will be found a 
comparison between the various standard wire gauges now employed, 
together with the nearest corresponding number of the millimeters, 





TIIE PROPERTIES OF WIRE. 


7 


Table No. 2.—Giving Relations between 


Imperial Standard Wire Gauge. Washburn and Moen’s Wire Gauge. 

Brown and Sharpe’s Wire Gauge. Trenton Wire Gauge. 

Birmingham or Stubbs Wire Gauge. Old English Wire Gauge. 


Gauge 

No. 


Diameter 

in Ten-Thousandths of an Inch. 


Diam. 

IN 

MMS. 

I. S. W. G. 

B.and S. 

W. G. 

B.orS.W.G. 

W. and M. 
W. G. 

Trenton 

W. G. 

Old Eng. 

7-0 

5000 

. . . 

. . . 




12.70 

6-0 

4640 

• • • 

• • • 

4600 

• . • 


11.78 

5-0 

4320 

• . • 

• • • 

4300 

4500 


10.97 

4-0 

4000 

4600 

4.540 

3930 

4000 


10.16 

3-0 

3720 

4096 

4250 

3620 

3600 


9.45 

2-0 

3480 

3048 

3800 

3310 

3300 


8.84 

1-0 

3240 

3249 

3400 

3070 

3050 


8.23 

1 

3000 

2893 

3000 

2830 

2850 


7.62 

2 

2760 

2576 

2840 

2630 

2650 


7.01 

3 

2520 

2294 

2590 

2440 

2450 


6.40 

4 

2320 

2043 

2380 

2250 

2250 


5.89 

5 

2120 

1819 

2200 

2070 

2050 


5.38 

6 

1920 

1620 

2030 

1920 

1900 


4.88 

7 

1760 

1443 

1800 

1770 

1750 


4.47 

8 

1600 

1285 

1650 

1620 

1600 


4.06 

9 

1440 

1144 

1480 

1480 

1450 


3.66 

10 

1280 

1019 

1340 

1350 

1300 


3.25 

11 

1160 

907 

1200 

1200 

1175 


2.95 

12 

1040 

808 

1090 

1050 

1050 


2.64 

13 

920 

719 

950 

920 

925 


2.34 

14 

800 

640 

830 

800 

800 

.0830 

2.03 

15 

720 

570 

720 

720 

700 

720 

1.83 

16 

640 

508 

650 

630 

610 

650 

1.63 

17 

560 

452 

580 

540 

525 

580 

1.42 

18 

480 

403 

490 

470 

450 

490 

1.22 

19 

400 

359 

420 

410 

400 

400 

1.02 

20 

360 

320 

350 

3.50 

350 

350 

.91 

21 

320 

284 

320 

320 

310 

315 

.81 

22 

280 

253 

280 

280 

280 

295 

.71 

23 

240 

226 

250 

250 

250 

270 

.61 

24 

220 

201 

220 

230 

225 

250 

.56 

25 

200 

179 

200 

200 

200 

230 

.51 

26 

180 

159 

180 

180 

180 

205 

.46 

27 

164 

142 

160 

170 

170 

187 

.42 

28 

148 

126 

140 

160 

160 

165 

.38 

l 29 

136 

113 

130 

150 

150 

155 

.34 

• 30 

124 

100 

120 

140 

140 

137 

.31 

31 

116 

89 

100 

135 

130 

122 

.29 

32 

10S 

79 

90 

130 

120 

112 

.27 

33 

100 

71 

80 

110 

110 

102 

.25 

34 

92 

63 

70 

100 

100 

95 

.23 

35 

84 

56 

50 

95 

95 

90 

.21 

36 

76 

50 

40 

90 

90 

75 

.19 

37 

68 

44 


85 

85 

65 

.17 

38 

60 

39 


80 

80 

57 

.15 

39 

52 

35 


75 

75 

50 

.13 

40 

48 

31 


70 

70 

45 

.12 

41 

44 






.11 

42 

40 






.10 

43 

36 






.09 

44 

32 






.08 

45 

28 






.u< 

46 

24 






.06 

47 

20 






.05 

48 

16 






.04 

49 

12 





. . 

.03 

50 

10 

. . . 

. . . 




.02 


















































8 


TIIE ELECTRICAL TRA NS MISS ION OF ENERGY. 


thus giving in a tabular form full information regarding the present 
method of wire measurement. 

10. The Circular Mil. — A convenient trade convention for the 

measurement of wire has arisen in the use of the so-called “ Circu- 

/ 

lar Mil,” the “ Mil ” being the name for the one-thousandth of an 
inch. The diameter, therefore, of a wire expressed in mils is its 
diameter in thousandths of an inch with the decimal point removed. 
If the diameter of any wire expressed in mils be squared, a number 
is obtained which is proportional to the actual area of the wire 
itself, and is termed the “circular millage ” of the wire. 

In Fig. 5 is the diagrammatic representation of a wire, each of the 
small circles symbolizing a unit wire, one mil, or one-thousandth of 

an inch, in diameter. It will be noticed that 
the diameter of the wire is ten small circles 
long, and therefore the wire is ten mils in 
diameter. The square of ten being 100, the 
circular millage of this wire would be 100 
circular mils. As the area of a circle is the 
square of its diameter multiplied by .7854, in 
order to convert the circular millage of any 
wire into its actual area in square inches, the 
circular millage must be multiplied by .7854, 
and the requisite decimal places pointed off. Thus, in the previous 
example, a wire of 100 circular mils has an actual area of .7854 X 
100 = .00007 square inches. Inasmuch as the circular millage is 
proportional to the actual area in square inches of the wire, it forms 
an exceedingly easy and convenient number for the purposes of cal¬ 
culation, and is widely used in this connection. 

11. Copper Wire. — It has only been within the last decade that 
the development of the uses of electrical energy has been sufficiently 
important to draw careful attention to the materials to be employed 
in line construction. Previously to 1880, electrical lines were almost 
exclusively confined to those used by the telegraph, which, with the 
exception of the submarine cables, were entirely constructed of iron 
wire. The electrical resistance of iron wire is some seven times 
greater than that of pure copper, yet it has only been within the last 
decade that the state of copper metallurgy was sufficiently advanced 
to render possible the production of pure copper in commercial 




THE PROPERTIES OE WIRE. 


9 


quantities. Experiment also indicated that very small quantities of 
various impurities increased the electrical resistance in an enormous 
ratio. This increase in resistance, due to the admixture of other 
substances, is indicated in Table No. 3. 

Table No. 3. 

Variation in the resistance of copper due to varying purity. 

Assuming pure copper to have a conductivity of 100 : — 


The best refined copper would be.99.0 

Alloy of copper and silver, equal parts.86.0 

Copper containing 4 per cent of silicon.75.0 

“ “ 12 “ “ “ U Q 

Silicon bronze wire.35.0 

Copper with 10 per cent lead.30.0 

Phosphor bronze.29.0 

Bronze containing 35 per cent zinc.21.0 

“ “ iron.16.0 

Aluminum bronze.12.6 

Siemens steel.12.0 

Arsenical copper containing 10 per cent arsenic.9.0 

Phosphor bronze with 10 per cent of tin.6.5 

Phosphor bronze with 9 per cent phosphorus.4.9 


From the preceding figures it will be very apparent that high 
electrical conductivity can only be obtained by the selection of the 
purest copper. It is not surprising, therefore, that the developments 
of electrical industries have been followed by a marked improvement 
in copper metallurgy. The cable extending between Calais and 
Dover, laid in 1851, had a conductivity of 42 per cent of that of pure 
copper ; the Atlantic cable of 1856 had 50 per cent ; the Red Sea 
cable in 1857, 75 per cent ; the Atlantic cable of 1865, 96 per cent. 
These figures give approximately the rate of improvement in the 
manufacture of copper for electrical conductors, but it was necessary 
to await the advent of the modern dynamo in order to produce elec¬ 
trically pure copper at such prices as would permit of a wide com¬ 
mercial application. As long as electrical circuits were confined to 
telegraphic transmission in which the currents used were exceedingly 
small, the amount of line resistance was not a very important factor. 
As soon, however, as the problem was presented of transmitting 















10 


THE ELECTRICAL TRANSMISSION OE ENERGY\ 


large quantities of electrical energy, it became imperative to seek 
some better material. At present the use of iron and steel wire is 
confined to circuits carrying but very small amounts of current, hard- 
drawn copper wire being universally adopted for lines having currents 
of any magnitude. 

12. To properly design an electrical circuit, all of the mechanical 
and electrical properties of the material to be used must be thor¬ 
oughly known. These properties for hard-drawn copper wire will be 
found in Tables Nos. 4, 5, and 6. In addition to its superior con¬ 
ductivity, copper presents a great advantage in durability. Even in 
the open country, and with all possible protection, iron rusts rapidly; 
while in the smoky air of most cities, iron lines rarely last more than 
three years, and cases have been known wherein iron wires have 
been entirely corroded within a few months. With copper, on the 
contrary, it is found that the wire becomes rapidly coated with a 
thin layer of sulphide of copper, probably not over one-thousandth 
of an inch in thickness, which seems to entirely protect the wire from 
any subsequent action. At any rate, no copper lines have as yet 
been in existence long enough for any perceptible corrosion to have 
made itself manifest. 

13. Composite Wire. — From time to time attempts have been 
made to use a composite wire, which should consist of a steel core, 
carrying an external sheath of copper ; the idea being that the steel 
interior would add sufficient tensile strength to enable long spans to 
be used, while the external covering of copper would provide the 
necessary conductivity for the current. To a certain extent these 
experiments have been successful ; but the use of composite wire 
has never extended beyond telegraphic or telephonic circuits, and 
now has fallen into disuse in the presence of the superior article 
of hard-drawn copper. 

In telephonic circles the idea of composite wire has just been 
revived, in the hope of improving the talking ability of long lines, 
by providing a medium of higher magnetic permeability. Theo¬ 
retically, a telephone circuit using a wire with a copper core and 
an iron sheath ought to talk better than the simple copper wire. 
Mechanical difficulties of manufacture, however, seem, so far, to be 
almost insurmountable to the commercial production of such a com¬ 
bination, only one German firm having succeeded in the manufac- 



I ABLE No. 4.-Properties of Copper Wire* 


'HE PROPERTIES OF WIRE. 


11 


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12 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Table No. 5.— Safe Currents for Paneled Wire. 

Applies to insulated copper wires of 98 c / 0 conductivity, carrying continuous cur¬ 
rents, encase! in wooden paneling, so that the temperature elevation of any 
wire shall net, with the proposed current, exceed 18° F. cr 10° C. 


Amperes. 

NoMEER 

IN 

B. & S. 

Circular 

Mils. 

Amperes. 

Number 

IN 

B. & S. 

Circular 

Mils. 

Amperes. 

Number 

in 

B. & S. 

Circular 

Mils. 

1,000 



2160900 

225 


297025 

15 

11 

8226 

900 



1876900 

200 

• • • 

254016 

12 

12 

6528 

800 



1612900 

174 

0000 

211600 

10.5 

13 

5184 

700 



1345600 

147 

000 

167805 

9.0 

14 

4110 

600 



1100401 

124 

00 

133079 

7.25 

15 

3260 

550 



976144 

103 

0 

105592 

6.00 

16 

2581 

500 



861184 

87 

1 

83694 

5.50 

17 

2044 

475 



804609 

73 

2 

66373 

4.00 

18 

1624 

450 



748225 

61 

3 

52634 

3.25 

19 

1253 

425 



692224 

52 

4 

41742 

2.75 

20 

1024 

400 



610000 

43 

5 

33102 

2.25 

21 

820 

375 



586756 

36 

6 

26244 

2.00 

22 

626 

350 



535824 

30 

7 

20822 

1.75 

23 

510 

325 



485809 

25 

8 

16512 

1.50 

24 

404 

300 



435600 

22 

9 

13110 

1.25 

25 

320 

275 



388129 

18 

10 

103S1 

1.00 

26 

254 

250 



342225 

. . . 

. . . 

. . . 

. . . 

. . . 

. . . 


Table No. 6. 

Fall of Potential in Copper Wire. 


Num¬ 

ber 

B. & S. 
Gauge. 

Circu¬ 

lar 

Mils. 

Fall of 
Potential 
in Volts 
per Am¬ 
pere PER 

1000 Feet. 

Num¬ 

ber 

B. & S. 
Gauge. 

Circu¬ 

lar 

Mils. 

Fall of 
Potential 
in Volts 
per Am¬ 
pere per 

1000 Feet. 

. Num¬ 
ber 

B. & S. 
Gauge. 

Circu¬ 

lar 

Mils. 

Fall of 
Potential 
in Volts 
per Am¬ 
pere per 

1000 Feet. 

0000 

211600.00 

.0505318 

5 

33102.00 

.3230183 

13 

5178.40 

2.064841 

000 

167805.00 

.0637158 

6 

26250.50 

.4073233 

14 

4106.80 

2.668524 

00 

133079.40 

.0303503 

7 

20316.00 

.5136713 

15 

3256.70 

3.208450 

0 

105592.50 

.1012593 

8 

13509.00 

.0476743 

16 

2582.90 

4.139673 

1 

83694.20 

.1277612 

9 

13094.00 

.8165943 

17 

2048.20 

5.220349 

2 

66373.00 

.1610920 

10 

10331.00 

1.03 

18 

1624.30 

6.582833 

3 

52634.00 

.2031469 

11 

8231.00 

1.293521 

19 

1252.10 

8.537567 

4 

41742.00 

.2561507 

12 

6529.90 

1.637494 

20 

1021.50 

10.46789 


ture. The cost of production also seems to more than compensate 
for the benefits derived. 

Attempts have also been made to use the various alloys of 
copper with silicon and phosphorus, known under the names of 
phosphor bronze and silicon bronze. While these alloys have very 
high tensile strength, in some cases exceeding 80,000 lbs. to the 

















































THE PROPERTIES OF WIRE . 


13 


square inch, their conductivity is so low that they have had but very 
little commercial extension. In a few cases electric railways have 
used silicon bronze for trolley wire, but the practice at the present 
time is almost exclusively confined to the adoption of hard-drawn 
copper. The properties of silicon bronze are given in Tables Nos. 
7a and 7 b (see following pages). 

14. Galvanizing and Tinning. — As a protection against cor¬ 
rosion, it is customary to coat iron and steel wire with a thin film 
of zinc, which, being not readily oxidized, serves as a barrier against 
the destructive action of the elements. While for open country 
lines this expedient is of considerable value, for city work galvan¬ 
izing has relatively but little importance ; for the various sulphur 
compounds, so largely present in the smoky atmosphere of towns, 
act with great rapidity on zinc, cutting away the film, and leaving 
the iron unprotected. Furthermore, with the best possible care in 
galvanizing, the coating is never perfectly continuous ; and subse¬ 
quent mechanical operations frequently cut through the zinc, expos¬ 
ing the iron, which immediately commences to oxidize. It has even 
been asserted that, in view of the inevitable discontinuity of the pro¬ 
tecting film, the zinc was a source of evil, forming with the iron a 
voltaic pair, thus aiding corrosion. 

The operation of galvanizing is accomplished by immersing the 
coil of wire in a pickling bath of dilute sulphuric acid, which serves 
to remove the scale, rust, and grease, leaving a chemically pure 
surface for the reception of the zinc. The coil is then placed upon 
a reel from which it is slowly unrolled, being drawn through a bath 
of molten zinc, the surface of which is covered with a layer of 
salammoniac or similar flux. It is necessary that the wire should 
be immersed in the bath for a sufficient time to become fully heated, 
in order that the zinc coating may be firmly coherent. As the wire 
emerges from the bath, the superfluous zinc is wiped away by means 
of an asbestos roller or similar device. Galvanized wire should be 
very carefully inspected to see that the zinc coating is, on the one 
hand, thoroughly continuous ; and that, upon the other, the super¬ 
fluous zinc has been carefully removed, freeing the wire from 
bunches and lumps, and leaving it with a smooth and polished 
surface. It is also advisable to test galvanized samples by immers¬ 
ing them for several minutes in a solution of sulphate of copper. 



14 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Table No. Ta. 


Properties of the Aluminum Brass and Bronze Co.’s Silicon Bronze Wire. 


Diameter in Inches. 

Sectional Area in 

Square Inches. 

Weight of one Mile 

in Pounds. 

Grade B. 
Silicon Bronze with 
a tensile strength of 
80,000 lbs. 
per sq. inch and a 
ductility of 110 
twists in 6 inches. 

Grade C. 

Silico i Bronze with 
a tensile strength of 
90,000 lbs. 
per sq. inch and a 
ductility of 75 
twists in 6 inches. 

Grade D. 

Silicon Bronze with 
a tensile strength of 
100,000 lbs. 
per sq. inch and a 
ductility of 60 
twists in 6 inches. 

Tensile 

Strength 

in 

Pounds. 

Resis¬ 
tance per 
Mile in 
Ohms. 

Tensile 

Strength 

in 

Pounds. 

Resistance 
per Mile 
in 

Ohms. 

Tensile 

Strength 

in 

Pounds. 

Resistance 
per Mile 
in 

Ohms. 

0.005 

.0000196 

.4 

1.6 

5119 

1.8 

5119 

2 

5119 

.010 

.0000785 

1.6 

6.3 

1280 

7.1 

1280 

8 

1280 

.015 

.0001767 

3.6 

14.1 

569 

16.0 

569 

18 

569 

.020 

.0003142 

6.4 

25.1 

320 

28.3 

320 

31 

320 

.025 

.0001909 

10. 

39.2 

205 

44.2 

205 

49 

204.7 

.030 

.0007069 

14.4 

56.6 

142 

63.6 

142 

71 

142.2 

.035 

.0003621 

19.6 

77.6 

105 

85.4 

105 

93 

104.5 

.010 

.0012566 

25.6 

100 

80 

113.0 

80 

126 

80. 

.015 

.0015904 

32.4 

127 

63 

143 

63 

159 

63.22 

.050 

.0019635 

40. 

157 

51 

177 

51 

196 

51.19 

.055 

.0023758 

48.4 

190 

42 

214 

42 

238 

42.32 

.060 

.0028274 

57.6 

226 

35 

254 

35 

283 

35.56 

.065 

.0033183 

67.6 

265 

30 

299 

30 

332 

30.33 

.070 

.0038484 

78.4 

307 

26 

346 

26 

385 

26.12 

.075 

.0044179 

90. 

353 

23 

400 

23 

445 

22.76 

.030 

.0050265 

102.4 

402 

20 

452 

20 

503 

20.00 

.035 

.0056745 

115.6 

454 

17.7 

511 

17.7 

567 

17.71 

.033 

.0063617 

129.6 

509 

15.8 

573 

15.8 

636 

15.80 

.035 

.0070882 

144.4 

567 

14.2 

638 

14.2 

709 

14.18 

.103 

.007854 

160.0 

628 

12.8 

707 

12.8 

785 

12.80 

.105 

.008659 

176.4 

693 

11.6 

779 

11.6 

866 

11.63 

.110 

.009503 

193.6 

760 

10.6 

855 

10.6 

950 

10.58 

.115 

.010387 

211.6 

831 

9.7 

935 

9. 

1039 

9.68 

.120 

.011310 

230.4 

905 

8.9 

1018 

8.9 

1131 ' 

8.88 

.125 

.012272 

250. 

982 

8.2 

1105 

8.2 

1227 

8.19 

.1 >3 

.013273 

270.4 

1062 

7.6 

1194 

7.6 

1329 

7.57 

.135 

.011314 

291.6 

1145 

7.0 

1288 

7.0 

1430 

7.03 

.110 

.015391 

313.6 

1232 

6.5 

1386 

6.5 

1539 

6.53 

.145 

.016513 

336.4 

1321 

6.1 

1486 

6.1 

1651 

6.08 

.150 

.017672 

360. 

1414 

5.7 

1591 

5.7 

1767 

5.69 

.155 

.018869 

384.4 

1510 

5.3 

1698 

5.3 

1887 

5.35 

.160 

.020106 

409.6 

1608 

5.0 

1810 

5.0 

2010 

5.00 

.165 

.021382 

435.6 

1711 

4.7 

1924 

4.7 

2138 

4.70 

.170 

.022698 

462.4 

1816 

4.4 

2043 

4.4 

2270 

4.43 

.175 

.024053 

490. 

1924 

4.2 

2165 

4.2 

2405 

4.18 

.130 

.025447 

518.4 

2036 

4.0 

2290 

4.0 

2545 

3.95 

.185 

.026880 

547.6 

2150 

3.7 

2419 

3.7 

2688 

3.74 

.190 

.028353 

577.6 

2268 

3.6 

2552 

3.6 

2835 

3.55 

.195 

.029865 

608.4 

2389 

3.4 

2GS8 

3.4 

2987 

3.37 

0.200 

.031416 

640. 

2513 

3.2 

2826 

3.2 

3142 

3.20 






































THE PROPERTIES OF WIRE, 


15 


Table No. 7a. — Continued . 

Properties of the Aluminum Brass and Bronze Co.’s Silicon Bronze Wire. 


Diameter in Inches. 

Sectional Area in 

Square Inches. 

Weight of one Mile 

in Pounds. 

Grade E. 
Silicon Bronze with 
a tensile strength of 
130,000 lbs. 
per sq. inch and a 
ductility of 45 
twists in 6 inches. 

Grade F. 

Silicon Bronze with 
a tensile strength of 
150,000 lbs. 
per sq. inch and a 
ductility of 30 
twists in 6 inches. 

Grade A. 

Comp. Silicon Bronze 
with a tensile strength 
of 75,000 lbs. 
per sq. inch and a 
ductility of 75 
twists in 6 inches. 

Tensile 

Strength 

in 

Pounds. 

Resis¬ 
tance per 
Mile in 
Ohms. 

Tensile 

Strength 

in 

Pounds. 

Resistance 
per Mile 
in 

Ohms. 

Tensile 

Strength 

in 

Pounds. 

Resistance 
per Mile 
in 

Ohms. 

0.005 

.0000196 

.4 

2.5 

10238 

2.9 

10238 

1.5 

2560 

.010 

.0000785 

1.6 

11.2 

2560 

11.9 

5620 

6. 

640 

.015 

.0001767 

3.6 

22.0 

1138 

26.5 

1138 

13.2 

285 

.020 

.0003142 

6.4 

40.8 

640 

47.2 

640 

23.6 

160 

.025 

.0004909 

10. 

63.8 

409 

73.6 

409 

36.8 

102 

.030 

.0007069 

14.4 

91.9 

284 

106 

284 

53 

71 

.035 

.0009621 

19.6 

120.3 

209 

139 

209 

70 

52 

.040 

.0012566 

25.6 

163 

160 

188 

160 

94 

40 

.045 

.0015904 

32.4 

207 

126 

239 

126 

120 

32 

.050 

.0019635 

40. 

255 

102 

295 

102 

148 

25 

.055 

.0023758 

48.4 

309 

85 

356 

85 

178 

21 

.060 

.0028274 

57.6 

367 

71 

424 

71 

214 

17.8 

.065 

.0033183 

67.6 

431 

61 

498 

61 

249 

15.2 

.070 

.0038484 

78.4 

500 

52 

577 

52 

289 

13.1 

.075 

.0044179 

90. 

578 

45 

667 

45 

334 

11.4 

.080 

.0050265 

102.4 

653 

40 

*754 

*40 

377 

10 

.085 

.0056745 

115.6 

738 

35 

856 

35 

428 

8.8 

.090 

.0063617 

129.6 

827 

31 

954 

31 

477 

7.9 

.095 

.0070882 

144.4 

921 

28 

1063 

28 

532 

7.1 

.100 

.007854 

160.0 

1021 

25 

1183 

26 

592 

6.4 

.105 

.008659 

176.4 

1127 

23 

1298 

23 

649 

5.8 

.110 

.009503 

193.6 

1235 

21 

1425 

21 

713 

5.3 

.115 

.010387 

211.6 

1350 

19.3 

1558 

19.3 

779 

4.8 

.120 

.011310 

230.4 

1470 

17.8 

1696 

17.8 

848 

4.4 

.125 

.012272 

250. 

1595 

16.4 

1841 

16.4 

921 

4.1 

.130 

.013273 

270.4 

1726 

15.1 

1991 

15.1 

995 

3.8 

.135 

.014314 

291.6 

1861 

14.1 

2147 

14.1 

1073 

3.5 

.140 

.015394 

313.6 

2000 

13.1 

2309 

13.1 

1155 

3.2 

.145 

.016513 

336.4 

2147 

12.2 

2478 

12.2 

1239 

3.0 

.150 

.017672 

360. 

2297 

11.4 

2651 

11.4 

1326 

2.8 

.1.55 

.018869 

384.4 

2453 

10.7 

2830 

10.7 

1415 

2.6 

.160 

.020106 

409.6 

2614 

10.0 

3016 

10.0 

1508 

2.5 

.165 

.021382 

435.6 

2780 

9.4 

3207 

9.4 

1603 

2.4 

.170 

.022698 

462.4 

2951 

8.9 

3404 

8.9 

1702 

2.2 

.175 

.024053 

490. 

3127 

8.4 

3608 

8.4 

1804 

2.1 

.180 

.025447 

518.4 

2309 

7.9 

3817 

7.9 

1908 

1.9 

.185 

.026880 

547.6 

3494 

7.5 

4032 

7.5 

2016 

1.8 

.190 

.028353 

577.6 

3686 

7.1 

4253 

7.1 

2126 

1.8 

.195 

.029865 

608.4 

3883 

6.7 

4480 

6.7 

2240 

1.7 

0.200 

.031416 

640. 

4084 

6.4 

4712 

6.4 

2356 

1.6 
























16 


THE ELECTRICAL TRANSMISSION' OF ENERGY. 


Table No. Tb. 

Table of Silicon Bronze Wire Weights and Electrical Resistances. 


Manufactured by the Phosphor Bronze Company, Limited. London. 


Nearest B. W. G. 

Diameter in Mils. 

Diameter in Millimeters. 

Sectional Area in Millimeters. 

Weight per Kilometer 

in Kilograms. 

Weight per Mile in Pounds. 

Quality A 
for Telegraph 
Lines, etc. 

Quality B 
for Railway 
Telegraphs, 

etc. 

Quality C 
for Telephone 
Lines, etc. 

Electrical Resistance 

at 0° C 

in Ohms per Kilo. 

Electrical Resistance 

at 32° F 

in Ohms per Mile. 

Electrical Resistance 

at 0° C 

in Ohms per Kilo. 

Electrical Resistance 

at 32° F 

in Ohms per Mile. 

Electrical Resistance 

at 0° C 

in Ohms per Kilo. 

Electrical Resistance 

at 32° F 

in Ohms per Mile. 

8 

158 

4.0 

12.5664 

112.00 

400 

1.32 

2.12 

1.54 

2.47 

• • • 


9 

148 

3.75 

11.0446 

98.44 

348 

1.51 

2.42 

1.83 

2.94 



9 

138 

3.50 

9.6211 

86.75 

301 

1.73 

2.77 

2.09 

3.35 



10 

128 

3.25 

8.2968 

73.94 

261 

2.01 

3.22 

2.43 

3.86 



11 

118 

3.0 

7.0685 

63.00 

223 

2.36 

3.78 

2.85 

4.57 



11 

114 

2.9 

6.6052 

58.87 

210 

2.53 

4.05 

3.05 

4.90 



11 

110 

2.8 

6.1575 

54.88 

195 

2.71 

4.33 

3.28 

5.25 



12 

10G 

2.7 

5.7255 

51.03 

181 

2.91 

4.65 

3.52 

5.64 



12 

102 

2.6 

5.3093 

47.32 

168 

3.14 

5.02 

3.80 

6.09 



12 

99 

2.5 

4.9087 

43.75 

155 

3.40 

5.44 

4.11 

6.60 



13 

95 

2.4 

4.5238 

40.32 

143 

3.69 

•5.91 

4.29 

6.90 



13 

91 

2.3 

4.1547 

37.03 

131 

4.02 

6.43 

4.46 

7.15 



13 

87 

2.2 

3.8013 

33.88 

120 

4.39 

7.02 

5.33 

8.55 



14 

83 

2.1 

3.4636 

30.87 

no 

4.82 

7.71 

5.82 

9.32 



14 

79 

2.0 

3.1415 

28.00 

100 

5.31 

8.50 

6.42 

10.30 

12.24 

19.60 

14 

75 

1.9 

2.8352 

25.27 

92 

5.89 

9.43 

7.00 

11.26 

13.56 

21.70 

15 

71 

1.8 

2.5446 

22.68 

82 

6.56 

10.50 

7.93 

12.70 

15.11 

24.18 

15 

G7 

1.7 

2.2698 

20.23 

73 

7.37 

11.79 

8.89 

14.25 

16.94 

27.00 

16 

63 

1.6 

2.0105 

17.92 

64 

8.31 

13.29 

10.04 

16.09 

19.13 

31.35 

17 

59 

1.5 

1.7671 

15.75 

55^ 

9.45 

15.12 

11.42 

18.30 

2L77 

35.00 

17 

. 55 

1.4 

1.5393 

13.72 

48 

10.85 

17.36 

13.11 

21.00 

24.98 

40.00 

18 

51 

1.3 

1.3273 

11.83 

42 

12.59 

20.14 

15.20 

24.40 

28.98 

46.00 

18 

48 

1.25 

1.2272 

10.93 

3S£ 

13.64 

21.82 

16.35 

26.19 

30. C5 

49.00 

18 

47 

1.2 

1.1309 

10.08 

36 

14.77 

23.63 

17.87 

28.80 

34.01 

54.00 

19 

43 

1.1 

0.9502 

8.47 

30 

17.58 

28.12 

21.24 

34.00 

40.47 

66.00 

19 

40 

1.0 

0.7854 

7.00 

25 

21.28 

34.00 

25.70 

42.00 

48.98 

79.00 

20 

36 

0.9 

0.6362 

5.67 

20 





60.46 

98.00 

21 

31 

0.8 

0.5026 

4.48 

16 





73.40 

118.00 


Any discontinuity in the coating is thereby immediately made mani¬ 
fest by a red spot of precipitated copper. Copper wire which is to be 
insulated with any of the rubber compounds should be protected by 
a coating of tin applied in a similar manner, for in the absence of 
this protection the sulphur universally present in rubber insulations 
is likely to combine with the copper. Indeed, there are cases on 
record where wires of small diameter have been by this cause 
entirely corroded away, and the circuit thus destroyed. Protective 














































THE PROPERTIES OP WIRE. 


IT 


circuits, such as those used for fire and burglar alarm signals, 
should be specially guarded against this evil. 

15. Insulated Wire. — Since the widespread introduction of 
currents of high pressure, it has become exceedingly important to 
protect all exposed wires with a sufficient coating of insulating ma¬ 
terial, so that such circuits may be rendered reasonably safe, and 
may not become sources of danger to human life. As a result, the 
wire manufacturers have adopted the custom of covering their prod¬ 
uct with insulating material of various kinds. This insulating 
•material usually takes the form of a hard braid, composed of either 
cotton or hemp woven onto the wire, and saturated with some of the 
compounds of india rubber, or with one of the pitches, tars, or resins. 
It is obvious that layer after layer of this insulating material may be 
wound upon the wire, so as to make a covering of almost any desired 
thickness. When selecting an insulating covering, great attention 
should be paid to its power of resisting abrasion. The greatest 
enemy to overhead electric circuits is found in the various tree 
branches which constantly, by the wind, are brought into contact 
with the wire, and tend to abrade and destroy the insulation. The 
insulating covering, therefore, should be tested by rubbing it against 
a coarse surface similar to the bark of a tree, and noting the time 
that is required to cut through and expose the wire. Where trees 
are numerous along the route, no fibrous insulation will stand for a 
long period of time. A very successful expedient, however, has been 
found in the device of covering the wire in its passage through the 
trees with a coating of bamboo. This coating is obtained by sawing 
ordinary fishing-poles longitudinally, and with a gouge cutting out 
the knots which occur in the cane. After being prepared in this 
manner the bamboo may be lashed upon the wire, and it is found 
that the hard silicious surface of the cane will resist for almost an 
indefinite period the abrasive action of swaying branches. Other 
attempts have been made to secure a reliable “tree-wire” by cover¬ 
ing the first coating of insulation upon the conductor itself, with an 
armor formed of a braid of steel wire, or a strip of iron or other 
metal, spirally wrapped around the insulation. Doubtless such ex¬ 
pedients could be made successful ; but in order to save expense and 
secure flexibility, the armor in the usual commercial forms is so light 
that it rarely survives, for a considerable period, the action of rust 


18 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


and abrasion. So, while the bamboo expedient is clumsy, it is suc¬ 
cessful. As insulated wire is usually sold by weight, information as 
to the gross weight per mile of the more common commercial forms 
becomes of value to the designer. In Table No. 8 the present 
commercial forms are tabulated. 

The insulating properties of a given covering are usually tested 
by coiling a length of the wire of from 100 to 1000 feet, depending 
on the quality of the insulation, in a tub of water, and measuring 
the leakage current with a sensitive galvanometer. If possible, the 
battery employed should have at least double the voltage of the 
current for which the wire is subsequently to be used. For tele¬ 
phone and telegraph cables, it is usual to use from 200 to 500 volts. 
For other circuits, the test is made with two or three times the volt¬ 
age that is to be used on the line. After prolonged soaking in the 
testing tub, the wire battery and galvanometer are joined up in series, 
the remaining pole of the battery being connected to a plate of metal 
placed in the tub, and the leakage current measured. While 100 
megohms per mile is a very common requirement, it is impossible, in 
view of the widely varying character of insulations and circuits, to 
give a definite standard. 

16. Flexible Cable. — In this country it is not uncommon to use 
wire in a single rod up to i inch in diameter. Large sizes are, how¬ 
ever, exceedingly stiff and difficult to handle, so that for greater 
diameters, and in many cases for \ inch or less, it becomes essential 
to use a stranded conductor in order to obtain the requisite flexibility. 
Twisted cables are from 10 to 15 per cent more expensive than 
solid conductors ; for, owing to the spiral arrangement of the strands, 
there is from 1 to 3 per cent more metal per unit of cross-section 
and length than in a solid conductor of equal resistance. The pro¬ 
cess of manufacture, also involving two or three additional handlings, 
adds to the cost ; and as the stranded conductor is more bulky, a 
considerably larger quantity of insulation is required. The ease of 
ereption, however, will in many cases, largely if not entirely, com¬ 
pensate for the increased expenditure in raw material in the stranded 
conductor. The properties of common commercial flexible cable may 
be found in Table No. 9. 

The use of flexible cable may obviously be avoided by stringing 
a sufficient number of separate wires, and joining them in multiple 


I 


19 


THE PROPERTIES OE WIRE. 



Table No. 8. 

Giving Approximate Weights per Mile of Various Insulated Wires. All IVeights are in Lbs. per Mile. 













































































































20 


T1IE ELECTRIC TRANSMISSION OE ENERGY. 










































































































































































Table No. 8. — Continued. 


21 


THE PROPERTIES OE WIRE. 


























































































































99 

4-J 


the electrical transmission of energy. 


arc, in order to make up the necessary copper section. In fact, this 
is the plan most usually adopted ; for all of the ordinary sizes of wire 
can readily be obtained in stock, while flexible cable is only made to 
order, at least in the larger sizes. The use of separate wires leads 
to greater expense in insulators, pole fixtures, greater weight of insu¬ 
lating material on the wire, and increased cost in stringing. Sepa¬ 
rate lines also entail a larger annual maintenance, so for all reasons 
cable is to be preferred when it is possible to obtain it. To facilitate 



Fig. 6. Tension Testing-Machine. 


calculation, Table No. 10 gives the circular millage of the various 
combinations of Nos. 000, 00, 0, 1 and 2 wire, from which a line of 
any copper cross-section may be calculated. After the total circular 
millage is found for the given line, it should be divided by 211,000 
(the area of a 0000 wire), the quotient will be the least number of 
0000 wires required ; if there is a remainder, find the nearest num¬ 
ber corresponding to it in the column headed “Circular millage” of 
Table No. 10, and in the column opposite will be found the least 
number and size of wires that will make up the required amount. 


























































TIIE PROPERTIES OE WIRE 


92 



Q 

CO 

p 

(0 

>1 

EL 

►3 

p 

cr 

co* 

o 


w 

CO 

h«5 

CO 

1-5 

CO 

►» 

h- 

o 

CO 


c 


02 

< 7 *- 

t-J 

P 

P 

CL 

CO 

JL 


Q 

p 

cr 


hJ 

J 


2 


cl 

Cfl 

71 

<33 

H 

X 

w 

o 

> 

5« 

33 

33 

n 


> 

fc> 


a 

Pi 


73 

> 


* 

7» 


















































































24 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


Table No. 10. 

Giving the Circular Millage of the Various Combinations of Nos. 1, 2, and 3 Wire. 


Circular 

Millage. 

Wire Combination. 

Circular 

Millage. 

Wire Combination. 

009 1 1 9 

3. 

u 

+ u 

+ * 

+1+2+3 

273339 

a + o 


5 5 0 4 8 5 

it 

0 

+ $ 

+ b 

+ 1 + 2 

255601 

b +1 

+ 2 

490112 

3 

0 

+ '§ 

+ b 

+ 1 

252080 

t+ 2 

+ 3 

476040 

3 

0 

+ li 

+ 1 

+ 2 + 3 

251499 

a + i 


441314 

•> 

0 

+ b 

+ 1 

+ 2 + 3 

238613 

z + b 


423406 

.3. 

0 

+ 0 

+ 1 

+ 2 

234178 

5+2 


400418 

3. 

0 

+ ff 

+ 4 


224541 

* + 2 

+ 3 

388080 

•) 

0 

+ b 

+ i 

+ 2 

220439 

f+ 3 


370500 

3 

0 

+ 1 

+ 2 

+ 3 

216773 

* + l 


357033 

3 

0 

+ o' 

+ 1 


202701 

1 + 2 

+ 3 

335780 

•> 

V 

+1 

+ 2 

+ 3 

1 9 9 4 5 2 

a+ 2 


322307 

2 

0 

+ 0 

+ 1 


189228 

* + i 


317872 

3 

0 

+1 

+ 2 


185713 

i + 3 


308235 

l 

0 

+1 

+ 2 

L Q 

I d 

171907 

o + 2 


300884 

1 

0 

+ 2 



1 5 0 0 0 7 

1 +2 


286812 

3 

0 

+ 2 

+ 3 


130328 

1 +3 


283146 

o 

0 

+ 1 

+ 2 


119007 

2 + 3 



17. Testing and Inspection. — In all large contracts for wire, it 
is customary to locate an inspector at the manufactory, whose busi¬ 
ness it is to examine and see that the product complies fully with the 
specification requirements. The inspector must be provided with a 
machine for making tension tests, one for tortional tests, a wire gauge, 
a slide wire bridge, and an accurate scale for determining the weight 
of coils. One form of the tension-machine is shown in F ig- 6 (p. 22). 

The apparatus consists of two clamps, by means of which the 
ends of each wire sample can be secured, a straining mechanism for 
applying a breaking stress to the sample, and a scale apparatus for 
measuring the force required to produce rupture. Though there are 
many other designs of this apparatus in commercial use, all embrace 
the same features. By the side of the specimen an apparatus is 
placed, consisting of two sliding scales, one of which is secured to 
the top of the sample, and the other to the bottom. As stress is 
applied to the wire it elongates, the amount being measured by the 
mutual displacement of the scales. The torsion testing-machine is 
indicated in Fig. 7. 

A set of iron ways carries two clamps, to which the sample to be 










THE PROPERTIES OE WIRE. 


25 


examined can be secured. One clamp being movable longitudinally 
permits the length of test piece to be varied at pleasure. The fixed 
clamp carries a spindle that, by means of a crank, can be rotated, thus 



twisting the specimen. To the spindle is attached a counting-wheel 
to register the number of twists required to produce rupture. In 
making all physical examinations great care should be taken to see 
that the test pieces are carefully set in the axis of the testing-ma¬ 
chine, that the stress is applied steadily and uniformly, and that the 
jaws do not injure the wire, thus giving rise to erroneous results. 

Fig. 8 illustrates the best and most useful form of wire gauge, 
in the shape of a micrometer. In skillful hands this instrument 
will give accurate results to a ten- 
thousandth of an inch ; and thus 
the actual size of the sample un¬ 
der examination may at various 
points be determined, and compared 
with the tabulated diameter of the 
desired gauge number. Deter¬ 
mination may also be made of 
the roundness of the wire. Care 

should be constantly exercised to always exert a constant, though 
light, pressure on the micrometer screw, that there may be no 
springing of the apparatus, and that uniform readings may be ob¬ 
tained. The slide wire bridge, for determining the electrical proper¬ 
ties of the samples under examination, will be found illustrated and 
described in the chapter on testing. For determining the weight 
of coils and the weight per mile, there is no better instrument than 
a good platform scale, carefully tested, and adjusted to be sensitive 
to a fraction of a pound. 



Fig. 8. Micrometer Wire Gauge. 















































26 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


18. Specifications for Line Wire. — As a guide to the selec¬ 
tion of line wire, the following specifications are the latest issue by 
the British Postal Telegraph authorities. 


I. SPECIFICATIONS FOR COPPER WIRE.' 

.S’. ‘ <(• 

dft, T r # . f 

In this specification, the term “piece” shall be understood to 
mean a single length of wire without joint or splice of any descrip¬ 
tion before being drawn, or in a finished wire ; a “coil ” shall be held 
to be a piece of wire in the form of a coil ; and a “parcel ” shall be 
any quantity of manufactured wire presented for examination and 
testing at any one time. 

1. The wire shall be drawn in continuous pieces of the respective weights 
and diameters given in the Table hereunto annexed (see Table No. 11), 
and every piece must be gauged for a diameter in one or more places. 

Table No. 11. 


Data accompanying British P. O. Wire Specifications. 


Weight per Statute 
Mile. 

Approximate Equiva¬ 
lent Diameter. 

Minimum 

Breaking 

Weight. 

Minimum 

Number 

of 

Twists. 

Maximum 
Resistance 
per Mile of 
Wire when 
Hard at 
60° F. 

Minimum 
Weight of 
Each Piece 
(or Coil) of 
Wire. 

Standard. 

Range 

Allowed. 

Standard. 

Range 

Allowed. 

Lbs. 

Lbs. 

Mils. 

Mils. 

Lbs. 


Ohms. 

Lbs. 

100 

974 

79 

78 

330 

T 30 

9.10 

50 


102£ 


80 


O) 



150 

146| 

97 

-N 9. >5 

490 

= 25 

6.05 

50 


153£ 


98 


CO 



200 

195 

112 

1104 

650 

6 20 

4.53 

50 


205 


113J 





400 

390 

158 

155^ 

1250 

7 25 

2.27 

SO 


410 


160A 





600 

585 

194 

191 

1800 

e 20 

1.484 

80 


615 


19G 





800 

780 

224 

220 £ 

2400 

~ 15 

1.113 

80 


S20 


226 






A maximum weight of 1>2 pounds for eacli coil is fixed for all sizes. 


2. The wire shall be perfectly symmetrical, uniform in quality, pliable, free 

from scale, inequalities, flaws, splits, and other defects, and shall be 
subject to the tests hereinafter provided for. 

3. Every piece may be tested for ductility and tensile strength, and 5% of 

the entire number of pieces may be cut and tested in any part. Pieces 
cut for this purpose shall not be brazed or otherwise joined together, 
but each length shall be bound up into a separate coil. 






















THE PROPERTIES OE WIRE. 



4. I lie wire shall be capable of being wrapped in six turns round a wire of its 

own diameter; unwrapped, and again wrapped in six turns round a wire 
of its own diameter in the same direction as the first wrapping, without 
breaking; and shall be also capable of bearing the number of twists 
set down in detail, without breaking. The twist-test is made as 
follows: 1 he wire will be gripped by two vises, one of which will 

be made to revolve at a speed not exceeding one revolution per second. 
I he twist thus given to the wire will be reckoned by means of an 
ink-mark, which forms a spiral on the wire during torsion, the full 
number of twists to be visible between the vises. 

5. I est for tensile strength may be made with a lever or other machine 
which has the approval of the officer appointed on behalf of the Post¬ 
master-General to inspect the wire, and hereinafter called the Inspecting 
Officer, who will be afforded all requisite facilities for proving the cor¬ 
rectness of the machine. 

6. I he electrical resistance of each test-piece shall be reduced according to 
its diameter, and shall be calculated for a temperature of (50° F. Such 
test-piece shall measure not less than one-thirtieth part of an English 
statute mile. 

7. If, after the examination of any parcel of wire, 5% of such parcel fail 
to meet all or any of the requirements of the specification and of the 
table, the whole of such parcel shall be rejected; and on no account 
shall such parcel, or any part thereof, be again presented for examina¬ 
tion and testing; and this stipulation shall be deemed to be, and shall 
be treated as, an essential condition of the contract. 

8. Each piece, when approved by the Inspecting Officer, shall be made into a 
coil, and be separately bound; and in no case shall two or more pieces 
be linked or otherwise jointed together. The eye of the coil shall be 
not less than 18 inches, nor more than 20 inches, in diameter. 

9. Each coil of approved wire shall be weighed separately, and its weight 
(in English pounds avoirdupois) stamped on a soft copper label, which 
shall be provided by the contractors, the label being firmly affixed to 
the inner part of the coil. The contractors shall also provide the 
assistance necessary for properly affixing to each coil of approved 
wire, under the direction of the Inspecting Officer, a metallic seal 
which shall be provided by the Postmaster-General, the weight of 
this seal being deducted from the invoiced weight of the wire when 
each delivery is made, or on completion of the order, as may be ar¬ 
ranged. 

10. The approved wire shall be wrapped in canvas, and be delivered as 
required, securely packed in casks or cases. 


28 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


II. SPECIFICATIONS FOR IRON WIRE. 

For iron wire the same general characteristics are required in so 
far as quality of wire and amount of testing and inspection are con¬ 
cerned. The physical requirements, however, will be found in 
Table No. 12. 

Table No. 12. 

The Specifications issued by the British Postal Telegraph Authorities for the Supply 

of Galvanized Iron Wire. 


Weight 

Mile. 

PER 

Diameter. 

Tests for Strenc 
Ductilitv. 

TH and 

Resistance per Mile of the 

Standard Size at 00° Fahr. 

Constant, 

being Standard Weight by Resistance. 

Weight 

of 

Each 
Piece, (or 
Coil). 

Required Standard. 

Allowed. 

Required Standard. 

Allowed. 

'v 

fcO 

22 

-cS 

<u 

u 

No. of Twists in 0 in. 

For Breaking Weight not less than 

No. of Twists i:i 0 in. 

For Breaking Weight not less than 

No. of Twists in 0 in. 

*5 

Maximum. 

Minimum. 

Maximum. 

Minimum. 

*— 

Minimum. 

Minimum. 

Maximum. 

Minimum. 

Maximum. 

Lbs. 

Lbs. 

Lbs. 

Mils. 

Mils. 

Mils. 

Lbs. 


Lbs. 


Lbs. 


Ohms. 


Lbs. 

Lbs. 

800 

767 

00 

W 

vw 

242 

237 

247 

2480 

15 

2550 

14 

2020 

13 

0.75 

5400 

90 

120 

000 

571 

629 

209 

204 

214 

1800 

17 

1910 

10 

1900 

15 

9.00 

5400 

90 

120 

450 

424 

477 

181 

170 

180 

1390 

19 

1425 

18 

1400 

17 

12.00 

5400 

90 

120 

400 

377 

424 

171 

10G 

170 

1240 

21 

1270 

20 

1300 

19 

13.50 

5400 

90 

120 

200 

190 

213 

121 

118 

125 

020 

30 

038 

28 

055 

20 

27.(Ml 

5400 

40 

65 


The most recent practice in American aerial line construction 
requires manufacturers to furnish line wire under the following 
requirements : — 

COPPER WIRE. 

1. Finish.— Each coil shall be drawn in one length and he exempt from all 

joints or splices. All wire shall be truly cylindrical and fully up to 
gauge specified for each size, and must not contain any scale, inequali¬ 
ties, flaws, cold shuts, seams, or other imperfections. 

2. Inspection.—The purchaser will appoint an inspector, who shall be sup¬ 

plied by the manufacturer with all facilities which may be required for 
examining the finished product, or any of the processes of manufacture. 
The inspector shall have the privilege of overseeing the packing and 
shipping of the samples. The inspector will reject any and all wire 
which does not fully come up to all the specification requirements. The 
purchaser further reserves the right to reject on reception, any or all lots 































































TIIE PROPERTIES OF WIRE. 


29 


of wire which do not fulfil the specifications, even though they shall pre¬ 
viously have been passed or accepted by the inspector. 

■). Apparatus.— I he manufacturer must supply, at the mill, the necessary 
apparatus tor making the examination called for. This apparatus shall 
consist ot a tension testing-machine, a torsion testing-machine, an elon¬ 
gation gauge, an accurate platform scale, and an accurate bridge and 
battery. Each of these pieces of apparatus may be examined by, and 
shall be satisfactory to, the inspector. 

4. Packing for Shipment. — When ready for shipment, each coil must be 

securely tied with not less than four separate pieces of strong twine, and' 
shall be protected by a sufficient wrapping of burlap so the wire may not 
be injured during transportation. The wrappings shall be placed upon 
th£ wire bundles, after they have been coiled and secured by the twine. 
The diameter of the eye of each coil shall be prescribed by the inspector, 
and all coils shipped shall not vary more than two inches in the diameter 
of the eye. 

5. Weight. — Each coil shall have its length and weight plainly and indelibly 

marked upon two brass tags, which shall be secured to the coil, one 
inside of the wrapping, and the other outside. 

6. Mechanical Properties.—All wire shall be fully and truly up to gauge 

standard, as per B. and S. wire gauge. The wire shall be cylindrical in 
every respect. The inspector shall test the size and roundness of the 
wire by measuring each end of each coil, and also by measuring at least 
four places in the length of each coil. A variation of not more than one 
and one-half mils on either side of the specified wire gauge number will 
be allowed, and the wire must be truly round within one mil upon oppo¬ 
site diameters at the same point of measurement. The strength of the 
wire shall be determined by taking a sample from one end of each coil, 
30" in length. Of this piece, 18" shall be tested for tension and elonga- 
gation, by breaking the same in the tension testing-machine. The sam¬ 
ples should show a strength in accordance with the following table : — 


Size of 

Breaking 

Breaking 

Size of 

Breaking 

Breaking 

Wire, 

Weight of 

Weight of 

Wire, 

Weight of 

Weight of 

B. & S. 

Hard-drawn. 

Annealed. 

B. & S. 

Hard-drawn. 

Annealed. 

Gauge. 

Lbs. 

Lbs. 

Gauge. 

Lbs. 

Lbs. 

0000 

0,971 

5,650 

9 

617 

349 

000 

7,907 

4,480 

10 

489 

277 

00 

G,271 

3,553 

11 

388 

219 

0 

4,973 

2,818 

12 

307 

174 

1 

3,943 

2,234 

13 

244 

138 

2 

3,127 

1,772 

14 

193 

109 

3 

2,480 

1,405 

15 

153 

87 

4 

1,967 

1,114 

16 

133 

69 

5 

1,559 

883 

17 

97 

55 

6 

1,237 

700 

18 

77 

43 

7 

980 

555 

19 

61 

34 

8 

778 

440 

20 

48 

27 






























30 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


A variation of H per cent on either side of the tabular limits will be ac¬ 
cepted by the inspector. The elongation of the wire must be at least 
3 per cent for all sizes larger than No. 1; 1-j per cent from No. 1 to No. 10, 
and 1 per cent for sizes less than No. 10, for hard-drawn copper wire. The 
remainder of the sample selected will be tested for torsion. The torsion 
sample will be twisted in the torsion testing-machine to destruction, one 
foot in length being placed between the jaws of the machine. Under 
these circumstances, hard-drawn copper wire shall show not less than 20 
twists for sizes over No. 1; from 40 to 90 twists in sizes from No. 1 to 
No. 10; and not less than 100 twists in sizes less than No. 10. Should 
the sample selected from one end of each coil show failure to come up to 
the specifications, the inspector may take a second sample from the other 
end of the coil. If the average of the results from both samples shall be 
within the specifications, the coil shall be accepted; if not within the 
specifications, the coil shall be rejected. The weight per mile shall be de¬ 
termined by carefully weighing 2 per cent of the number of coils called 
for in the contract; and the weight thus obtained shall correspond, within 
2 per cent, on either side of the result given in the following formulae: — 

CM 

\\ eight per mile =-; 

& 1 02.567 

Weight per 1000 ft. = o / . 

7. Electrical Properties. — The electrical properties of the wire shall be 
determined by the inspector, selecting 3 per cent of the coils, and from 
them taking lengths of 100 ft., 500 ft., or 1000 ft., at his discretion, and 
measuring the conductivity of the same with a standard bridge. For 
soft-drawn copper wire, the following resistance per mil ft. will be 
assumed : — 


Temperature 

in Degrees 

F. 

Resistance 

Legal Ohms. 

Temperature 

in Degrees 

F. 

Resistance 
Legal Ohms. 

0 

8.90707 

00 

10.20253 

10 

9.10413 

70 

10.42083 

20 

9.36473 

80 

10.04208 

30 

9.50887 

90 

10.86800 

40 

9.77655 

100 

11.09698 

50 

9.98777 




For hard-drawn wire, the resistance per mil ft. shall be 1.0226 times the 
foregoing figures. All wire shall be within 98 per cent of the above 
figures. 

8. Requirements for Iron Wire. — All iron wire shall be subjected to the 
same general requirements as above specified for copper wire, and shall 
be inspected and tested in the same general manner. The wire shall be 
carefully annealed, without burning or undue rusting from the heat of the 













THE PROPERTIES OF WIRE. 


31 


furnace. It shall be soft, pliable, and capable of elongating not less than 
15 per cent in lengths of one foot between the jaws of the testing- 
machine. 

1). Mechanical Properties. — Weights and strengths of the various sizes shall 
be as follows : — 


Number 

B. W. G. 

Weight 
per Mile. 

Breaking 
W EIGHT. 

N UMBER 

B. W. G. 

Weight 

per Mile. 

Breaking 

Weight. 

4 

730 

1898 

10 

260 

676 

6 

540 

1404 

11 

214 

556 

8 

380 

988 

12 

165 

429 

9 

330 

a r >8 

14 

96 

250 


In general the weight per mile shall be CJ//72. High tensile strength is 
not required ; but, in general, wire must not break under less strain 
than two and one-half times its weight per mile in pounds. 

10. Torsion Tests.—Torsion tests will be made as prescribed for copper wire, 

and the specimens must not fail under less than 80 twists in a length of 
one foot. In the mechanical requirements for iron wire, a variation of 
3 per cent on either side of the specification limits will be accepted by 
the inspector. 

11. The electrical resistance of iron wire will be determined in the same man¬ 

ner as specified for copper wire, excepting that the resistance of the iron 
wire shall be 6.081 times the resistance of the copper wire per mil ft. at 
32° F., with an allowance of .278 per cent for every degree of increase 
of temperature. 

12. Galvanizing. — When galvanized wire is called for, the galvanizing must 

be true and smooth over the entire length of all the coils, showing that 
the zinc has been carefully and evenly wiped oft. The wire must show 
no black spots, scales, or inequalities. The galvanizing will be tested 
by plunging a sample of wire from 5 per cent ot all the coils into a 
saturated solution of sulphate of copper, and permitting same to re¬ 
main for 70 seconds. The wire will then be withdrawn and wiped 
clean. This operation will be repeated four times, at the end of which 
time, if the wire appears black, the galvanizing will be considered satis¬ 
factory, and the sample accepted. If, on the contrary, any precipitated 
copper is shown, the galvanizing will not be considered sufficiently well 
done, and the samples may be rejected. 


19. The Tension of Aerial Lines. — When a wire is stretched 
between the points A and B, Fig. 9, situated at the same level, it 
describes a curve ADB, known under the name of the catenary. 

The horizontal distance AB is termed the span, while the verti¬ 
cal distance CD between the lowest point of. the curve and the 















32 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


horizontal line AB is the deflection. The catenary may be re¬ 
ferred to two rectangular co-ordinates, of which the vertical axis 
O y passes through the lowest point of the curve, while the horizontal 



Fig. 9. Diagram of the Catenary. 


axis is situated at such a distance “ k,” beloiv the point D, or the 
lowest part of the curve, that if the tension of the wire at this point 
be represented by T, and the weight per unit of length by P, then 


// 


T 
P ' 



Under these conditions the equation of the catenary may be 
represented by 


v = 


h 

9 


+ e 


( 2 ) 


in which e is the base of the Napierian system of logarithms. Devel¬ 
oping the second number of this equation by McLaurin’s formula, 


y — k [ 1 + 


x 


l/J./r I.2.3.4.// 4 


—etc. 



Usually the tension T is so large in respect to the weight P that 
for all ordinary spans it is sufficient to represent the curve by the 
following equation, which is readily recognized as that of a parabola, 


X‘ 


W 


v = h + - 
2 h 

Calling the span a , the deflection f and making x — -, from equa¬ 
tion (4), 











THE PROPERTIES OF WIRE. 


33 


This last equation gives the deflection at the center, if the weight 
per unit of length is known, as well as the span and the tension at 
the lowest point. If the span, the deflection, and w r eight are known, 
it is easy to calculate the tension. The tension T h at the highest 
pomc\_s given by the equation 


T h =T+ Pf (7) 

Except in cases where the deflection is very great, the tension T h 
does not sensibly differ from the tension T at the lowest point ; and 
without serious error it may be assumed that the tension calculated 
by formula (6) represents the tension throughout all points of the 
span. The length of the wire may be obtained from the equation 


dl — a/ dx l -f dy 1 = dx 
Substituting for dyjdx its value from equation (4) 


I +(I) - 


dl = dx ( 1 + ) = dx ( 1 + lEi - irrT + etc 


X~ 


h 


2 Jv 


8// 


an expression that for common spans reduces to 

dl = dx ^1 + integrating, 

= /h"K 1 + •*#i =a+i 


i 


24 Id 


o » 


or 


l = a + - 
1 * 


PI 


y-2 


24 T 1 


(8) 

(9) 

( 10 ), 

( 11 ) 



If a equals the horizontal span, / the actual length of the wire be¬ 
tween the insulators,/the deflection of the wire at the center, P the 
weight of one unit of length of the wire, and T the tension of the wire 
at its lowest point, the three following equations are approximate : — 

1 2 3 

f = fj. (13) T = ^ (14) / = « + |£ (15) 

20. Influence of the Variations of Temperature. — 1 he ten¬ 
sion in the wire deduced from these formulae is obviously the tension 
at the time when the line is erected. If the temperature falls, the 











34 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


wire tends to contract in proportion to the diminution of tempera¬ 
ture. The elasticity of the wire, however, allows it to elongate 
somewhat under any increase in the tension that results from the 
contraction. The accumulation of sleet or snow upon the wire adds 
a very considerable amount to its weight, and consequently to the 


Table No. 13 . 

Sags and Tensions to be Observed in Erecting Wires at Various Temperatures. 

400 lbs. Iron Wire (No. 7-j). 




22° 

F. 


40° F. 


58° F. 


76° 

F. 

Span 


Low Winter 

Ordinary Winter 

Averag 

e Summer 

High Summer 

IN 

Temperature. 


Temperature. 


Temperature. 

Temperature. 

Feet. 


























Sag. 

Tension. 

S 

i 

ag. 

| Tension. 

Sag. 

Tension. 

1 

Sag. 

Tension. 


Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

300 

3 

1! 

270 

3 

9 

227 

4 


200 

4 

85 

180 

270 

2 

6| 

270 

3 

1! 

219 

3 

2| 

190 

4 

<'I 

1G9 

240 

2 

n 

270 

2 

75 

210 

3 


178 

3 

0 ® 

157 

210 

i 

GA 

270 

2 

n 

198 

2 

GA 

1G4 

2 

101 

143 

180 

i 

n 

270 

1 

8 

184 

9 

05 

148 

2 

45 

128 

150 

0 

9? 

270 

1 

Q1 

1G5 

1 

75 

130 

1 

115 

110 




150 Lbs. Hard-Drawn Copper 

Wire 

(No. 12^). 





22° 

F. 


40 

c F 


58 

0 F 


76° 

F. 

Span 


Low Winter 

Ordinary Winter 

Average Summer 

High Summer 

in 

Temperature. 


Temperature. 


Temperature. 

Temperature. 

Feet. 













Sag. 

Tension. 

Sag. 

Tension. 

Sag. 

Tension. 

Sag. 

Tension. 


Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

300 

2 

8 

120 

3 

7 

89 

4 

35 

74 

4 

Hi 

G4 

270. 

2 

2 

120 

3 

i 

84 

3 

9A 

0>9 

4 


GO 

240 

1 

sa 

120 

2 

<ii 

80 

3 

91 

-5 

G4 

O 

»> 

85 

54A 

210 

1 

3f 

120 

2 

ij 

73 

2 

8| 

57 A 

3 

91 

“2 

49 

180 

0 

HI 

120 

i 

9 

GG 

2 

35 

51 

2 

84 

43 

150 

0 

8 

120 

i 

n 

58 

i 

10 

44 

2 

25 

30A 




100 Lbs. Hard-Drawn Copper Wire (No. 14) 






22° 

F. 


40 

F. 


58 

F. 


76° F. 

Span 

Low Winter 

Ordinary Winter 

Average Summer 

High Summer 

in 

Temperature. 

Temperature. 

Temperature. 

Temperature. 

Feet. 













Sag. 

Tension. 

Sag. 

Tension. 

Sag. 

Tension. 

Sag. 

Tension. 


Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

Ft. 

In. 

Lbs. 

300 

2 

8 

80 

3 

rr 

i 

59 

4 

35 

49 

4 

Hi 

43 

270 

2 

2 

80 

3 

1 

5G 

o 

O 

H 

4G 

4 

45 

40 

240 

i 

8i 

80 

2 

6] 

53 

3 

Ol 

42V 

3 

85 

36 

210 

i 

3| 

80 

2 

lj 

49 

2 

05 

l -s 

38 

3 

2 A 

33 

180 

0 

U® 

80 

i 

9 

44 

2 

Qi 

^8 

34 

2 

85 

29 

150 

0 

8 

80 

i 

J.6 

39 

i 

10 

29 

2 

n 

24 





































































































THE PROPERTIES OE WIRE. 


35 


tension to which it is subjected. In order to ensure against acci¬ 
dents, it is therefore necessary to so adjust the tension of the wire 
when the line is erected, that under all ordinary circumstances no 
future stresses will be sufficient to exceed the elastic limit of the 
material. The limiting tension permissible is often assumed to be 
from one-fifth to one-quarter of the breaking-strain, the limit of elas¬ 
ticity usually being about one-third of the ultimate strength. Lines 
which are erected in the summer time should be allowed a much 
greater deflection than those placed in the winter, in order that the 
contraction due to cold weather may not cause the tension to exceed 
the safety limit. Long spans must have more slack than short ones, 
and straight lines must be given more deflection than those in which 
curves are of frequent occurrence ; for the curve allows the line to 
give somewhat under the additional stresses introduced by contrac¬ 
tion. While slack lines are safer so far as the tension on the wires 
is concerned, they are liable to give extreme trouble from swinging 
crosses, and from entanglement with neighboring wires. In Table 
No. 13 will be found data indicating the appropriate deflections and 
tensions to be observed in stringing the more common sizes of iron 
and copper wire at the various temperatures to be met with in 
practice. 


36 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


CHAPTER III. 

CONSTRUCTION OF AERIAL CIRCUITS. 

PART I. —GENERAL LINE WORK. 

Art. 21. Classification. — Assuming the location of the central 
station as selected, and the general design of the plant determined, 
the construction of the necessary circuit becomes a matter for con¬ 
sideration. Electrical circuits may be primarily divided into Aerial 
and Underground, depending upon whether the line is placed upon 
poles distributed over the surface, or carried through a conduit or 
other structure buried in the earth. Either form of circuit may be 
further classified as Metallic or Grounded. In the metallic circuit, 
the entire line is composed of wire extending from one pole of the 
generating-station back to the other pole. In the grounded circuit, 
a portion of the line is composed of wire, while for the remainder the 
earth as a return is used. Depending on the design of the plant, 
electrical circuits may still further be catalogued as Telegraph cir¬ 
cuits, Telephone circuits, and Power circuits ; and the latter group 
may still further be subdivided into Lighting circuits, Motor circuits, 
and Railway circuits. 

22. Aerial Lines. — Recently all electrical circuits were of the 
aerial type ; as it has only been within the past decade that the in¬ 
creasing multiplicity of overhead wires has caused the various forms 
of conduit to spring into existence, that the streets of the larger 
cities might be freed from the inconvenience of pole circuits. 

23. Poles. — Aerial lines are built by setting upright into the 
ground poles of sufficient strength to carry the weight of wire neces¬ 
sary for the circuits, and the various lines are supported on insulators 
placed on cross-arms attached to the tops of the poles. P'or open 
country lines wooden poles are used, white Canadian cedar, Northern 
pine, or chestnut being considered the best material. In the South, 
cypress or Southern pine is common ; but it does not weather as 
well as the Northern woods. The poles should be sound, live wood. 


CONSTRUCTION OF AERIAL CIRCUITS. 


37 


straight and true, and free from bad knots, shakes, large cracks, 
dry rot, and other defects. The poles should not be less than six 
inches in diameter at the top for lines through the open country, or 
from seven to eight inches for city work. The bark should be 
carefully stripped from the poles, which should then be shaved and 
trimmed, and the gains for the cross-arms cut. It is also customary 
to bolt the cross-arms to the poles previous to setting, as it is con¬ 
siderably more economical for this work to be performed on the 
ground level. The distance apart at which poles are set varies 
greatly with the nature of the line, and territory through which it is 
constructed. For light lines in the open country, from thirty-five to 
forty-two poles per mile is a common rule. For heavier city lines, 
forty to fifty poles per mile is usual; while for electric railway work, 
from forty-five to fifty-five poles to the mile are necessary. 

24. Methods of Preservation. — In this country it is not cus¬ 
tomary to treat the poles in any way in reference to their preservation, 
excepting to give them one coat of paint previous to, and one after, 
erection. In Europe the custom of creosoting, or of treating them 
with various preserving solutions, is quite common. Besides the 
operation of creosoting, several methods of preservation have been 
suggested, which consist in soaking the poles in large tanks filled with 
solutions of chloride of zinc, chloride of mercury, sulphate of iron, 
or sulphate of copper. It is the attempt of all of these processes to 
make the preserving solution saturate the wood, and form, with the 
various vegetable albumens, insoluble compounds, thus lengthening 
the life of the timber. With the exception of creosoting, all these 
methods involve considerable expense, and as yet have not given 
results that seem to justify the necessary outlay. Recently the 
process of “Vulcanizing,” which simply consists in heating the poles 
for some hours in a closed cylinder to about 500° F., has given great 
satisfaction. The high temperature seasons the wood by coagulating 
the albumen, adding greatly to the life of the pole. The simplicity 
and cheapness of this process are greatly in its favor. 

The treatment by the creosoting process consists in placing the 
poles in a strong iron vat from which the air can be exhausted. In 
the vacuum thus produced, all the sap and other juices of the wood 
flow outwards, and are carried away by a suitable system of piping. 
Live steam at a pressure of about 100 pounds to the square inch 


88 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


is then admitted into the cylinder, and the poles thoroughly cooked 
and steamed for several hours. Subsequent to the steaming, crude 
petroleum oil is admitted into the cylinder under a hydrostatic 
pressure of 200 to 800 pounds. By means of this operation it is 
expected that all the fluids contained in the woods are extracted, 
and are replaced by the crude petroleum, contributing very materially 
to the life of the poles. Experiments have shown that lines con¬ 
structed of poles treated in this manner are in perfectly good con¬ 
dition after twenty years of life. 

25. The Height of Poles. — The height of the poles which it 
is necessary to use will depend very largely upon the magnitude or 
number of circuits which they are to sustain. For ordinary city 
work, for telegraph or telephone construction, a height of 40 to 60 
feet is usually employed. In some cases, however, very notably in 
some of the large metropolitan lines, poles of 100 or even 125 feet 
in height have been erected, carrying a very large number of wires. 
Usually it is preferable to use a high pole rather than a low one, in 
order that the line may be thoroughly clear of the street, and may 
not become too much of an obstruction to neighboring buildings. 

26. Cross-Arms. — The cross-arms, carrying insulators, should 
preferably be of yellow pine ; they should be carefully sawed, true 
and square, and should be of sound hard wood, and thoroughly coated 
with mineral paint having good insulating properties. The cross- 
arms are usually 4 4 " x 3|", and vary from 8 to 10 feet in length, 
depending upon the number of insulators to be supported. Two 
wires are carried on a three-foot arm, and 10 on a ten-foot arm. 
The top of the arm is rounded with a circular chamfer, as shown at 
C, Fig. 10, to prevent the accumulation of snow and water. Fre¬ 
quently the arms, including the pins, are assembled at the factory and 
shipped complete. The cross-arms are usually set 2C" apart vertically 
along the gains, strongly bolted and braced. Two braces are allotted 
to each arm. They are of galvanized iron, 1wide, thick, and 28" 
long. One end of each of the pair of braces is secured to the pole by 
one of the cross-arm bolts, the other ends being attached to the next 
arm above, between the second and third pin on the right and left hand 
of the pole, thus forming a bracket to steady the arm. It has been 
customary to secure the arm to the pole by means of two lag-bolts 
passed through the arms, and screwed into the pole. As the thread 


CONSTRUCTION OF AERIAL CIRCUITS. 


39 


of the lag-bolt destroys the fiber of the pole to such an extent that 
it is usually impossible to replace cross-arms after the line has been 
some years in service, it is at present considered better to fasten 
the arm with a single carriage-bolt, passed entirely through both arm 
and pole, the bolt hole being cleanly bored with a sharp bit, accu- 
l atcly to fit the bolt. The bearings of the bolt-head and nut should 
be prevented from crushing the wood by ample washers. In lines 
constructed of machined poles, as in street railway work, when the 
pole-tops are all uniform in size, the cross-arms may best be fastened 
by means of a U-bolt that extends entirely around the pole. This 
method obviates any injury or weakening of the pole itself. 

27. Pins. — The insulator pins should be of locust or oak. The 
pins have a turned shank l£" in diameter to fit the hole in the cross- 



c 


Fig. 10. Cross-Arms and Pins. 

arm, and when in place are secured by a single wire nail driven 
through the arm. The upper part of the pin is threaded to match 
the particular insulator for which the line is designed. Where 
corners in the line occur, the sustaining power of the pin is re-en¬ 
forced by securing it to the arm by a nut and washer. A corner pin 
is indicated at B, Fig. 10, and a common pin at A. The pins are 
placed 10" to 12" apart on the arm, with an allowance of 15" 
between the two middle pins, in order that the wires supported by 
them may adequately clear the pole. The general aspect of a 
properly equipped wooden pole-top, for telephone or telegraph lines, 
is shown in Fig. 11 (p. 38). 

28. The Facing of Arms. — In setting the poles, it is custom¬ 
ary to place the cross-arms in such a manner that those on the 

























40 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


adjacent poles shall face each other, while on the next two poles 
they shall be turned back to back. The object of this disposition 
of the cross-arms is to prevent accident in case of the breaking of 
any of the wires. If the cross-arms were all set in one direction, 
an excessive stress, or some accidental cause, such as a broken 
pole, might wrench off one of the cross-arms, and the stress being 
transferred to the next one, like a row of blocks the whole line 
would go down. On the contrary, if the arms are set alternately 
facing and back to back, it is practically impossible to pull off more 



than two sets of arms, and thus, frequently, a broken pole is kept 
from falling, and the line saved. To obtain good appearance, the 
poles should be carefully set plumb and true, leaving their tops 
essentially in a straight line. In city work this condition can 
usually be attained by using poles of the same height. In the open 
country, owing to the differences in level, it is essential to use poles 
of correspondingly varying heights in order to preserve uniformity. 

29. Stresses. — The stresses to which a pole-line is subjected 
are primarily due to the weight of the wire and cable which the 
poles have to support, and to the longitudinal stresses due to the 
























CONSTRUCTION OF AERIAL CIRCUITS. 


41 


tension upon them. Concerning the stresses to which the poles 
are subjected, the forces may be divided into three classes. 

30. First. — In straight line work the cross-arms and insulators 
transmit to the poles the weight of the wire and cables supported 
upon them. This stress acts vertically, being a direct load tending 
to break the arm at the center where it is secured to the pole, and 
to crush the pole as a column. In the winter, the weight thus 
thrown on poles may be very largely augmented by snow or sleet, 
with which the wires may become incrusted. 

31. Second. — The action of the wind against the wires de¬ 
velops considerable lateral stress, which causes the poles to vibrate 
in a dangerous manner, and may break them at or near the surface 
of the ground. 

32. Third. — Whenever a change of direction occurs in a pole¬ 
line, or wherever one or more wires or cables are terminated, the 
poles are subjected to a bending-stress, equivalent in the first case 
to the resultant of the tension in all of the circuits, pulling the poles 
sidewise ; and in the second case, to a bending-moment derived from 
the sum of all the tensions in the wires, or other circuits which are 
ended, tending to pull the pole over longitudinally in the direction 
of the line. 

Great care must be exercised in the design of all lines of magni¬ 
tude, to see that, at the points of change of direction, or at the 
termination of any or all circuits, the poles are sufficiently strong 
or carefully braced to withstand these stresses. 

In the case of a change of direction in a pole-line, the resultant 
of the line stress may be readily determined by the application of 
the well-known principle of the parallelogram of forces. By examin¬ 
ing the tensions in the line on either side of the angle, and determin¬ 
ing the resultant, the magnitude of the force tending to deflect the 
pole, and its direction, are readily ascertained. To counterbalance 
this tendency, the pole must be either stiff enough to stand the 
bending-moment, or else the top of the pole must be anchored 
in a direction opposed to the resultant stress, by means of a guy 
wire or rod. 

33. Calculations for Pole Strength. — A pole subjected to a 
horizontal force is- bent in the direction of the force; the fibers of 
the wood lying on the side of the pole toward the force being ex- 


42 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


tended, and those on the opposite side being compressed. If the 
pole be cylindrical, the section of rupture is at the surface of the 
ground. If, as is usually the case, the pole be a truncated cone, 
rupture occurs at the surface of the ground when the diameter of 
the pole at the point of application of the force is equal to, or 
greater than, § of the diameter at the surface of the ground. When 
the diameter of the section at the point of application of the force 
is less, the rupture takes place above the surface of the ground, at 
that point where the diameter is § of the diameter at the point of 
application of the force. 

The horizontal force which a pole will support at the instant 
of rupture, when the section of rupture coincides with the section 
at the ground level, is shown by the formula — 


where ft is the radius of the section at the surface of the ground, L 
is the height above the soil of the point of application of the force, 
and T x is the resistance to rupture per unit section of the substance 
which forms the pole. 

Transposing and assuming 10 as a factor of safety, the formula 
becomes 



( 17 ) 


Where the diameter of the section at the point of application 
of the force is less than § of the diameter at the surface of the 
ground, and the section of rupture is above the ground level, the 
force F which will rupture the pole is given by the more complicated 
formula — 



( 18 ) 


in which ft is the radius of the section at the surface of the ground, 
and ft x the radius of the section at which the force is applied. F\ in 
all cases, is the resultant of the horizontal forces acting on the pole, 
and a factor of safety of from 6 to 10 should be used. 

The value of T x may be found in Tables Nos. 14 and 15, com¬ 
piled from standard authorities, which give the ultimate or breaking 
load of various kinds of wood, either in tension or compression. 







CONSI'RUCTION OF AERIAL CIRCUITS. 


43 


Table No. 14 . 

Tensile Strength of Timber. 


Variety. 

Breaking Weight Per 
Square Inch in Lbs. 

Ash. white 


17,000 

Ash. American . 


17.000 

Ash. English 


10,000 

Beech . 


12,000 

Birch. 


15,000 

Cedar, Lebanon . 


12,000 

Cedar, West Indian 


7,500 

Cedar, American. 

. 

11,400 

Chestnut. 


P’,,000 

Cypress .... 


0,000 

Deal, Christiania. 


12,900 

Elm. 


10,000 

Oak. 


10,000 

Pine, pitch. 


7,000 

Pine, Riga. 


14,300 

Pine, yellow. 


12,000 

Pine, red. 


3,000 

Poplar . 


7,000 

Redwood, California . 

. 

10,800 

Spruce. 


10,000 

Sycamore . 


13,000 


Table No. 15 . 

Crushing Strength of Timber. 

Crushing Weight in Lbs. 


Variety. 

Per Square 

Inch. 

Ash . 


8,000 

Beech . 


7,700 

Birch. 

. . . . 4,500 “ 

6,000 

Cedar, red. 

. . . . 4,500 “ 

5,900 

Chestnut. 


5,350 

Elm. 


10,000 

Oak, American, white . 

. . . . 4,000 “ 

9,000 

Oak, English. 

, . . . 6,500 “ 

9,500 

Oak, Dantzic. 


7,700 

Pine, pitch. 


6,800 

Pine, yellow. 


6,500 

Pine, red. 

, . . . 6,000 “ 

7,500 

Pine, white. 

, . . . 5,000 « 

6,000 

Spruce, white. 

, . . . 4,500 “ 

6,000 



































44 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


34. The preceding formulae are generally applicable where the 
forces acting on a pole may be resolved into one horizontal com¬ 
ponent. Often the horizontal force is exceedingly large, as in a 
corner or terminal pole. In such cases, an unsupported pole of 
sufficient strength would be impracticable. By staying the pole with 
a guy-rod, a new set of conditions arise. Where a pole stands with¬ 
out guying, one-half of its fibers are in tension and the other half in 
compression. When the guy-rod is added, all the fibers of the pole 
are under compression, while the guy-rod is under tension. 

Let F equal the known horizontal resultant of the forces which 
act on the pole ; (3, the angle between the guy-rod and the ground 
level (horizontal) ; a, the angle between the guy-rod and the pole 
(perpendicular) ; T, the tension on the guy-rod ; and S, the crushing- 
force acting on the pole. 


Then, 


T 


F 


cos /3 


(19). 


and S = 7’ cos a. 


( 20 ) 


These formulae are true, assuming that the guy-rod is attached 
to the pole at the point of application of the horizontal resultant 
force F. 

Represent by P the total weight of pole cross-arms, guy-rod, 
fixtures, wires, and cables. The total crushing-force W acting on 
the pole is then S P. 

Considering the pole now as a long column fixed at one end, in 
which / is the distance in feet from ground to section just below 
cross-arms ; d is the diameter in inches of the smallest section of the 
pole below the cross-arms ; Hodgkinson’s experiments indicated that 
the ultimate supporting power is given for pine columns by the 
expression, — 

W (in short tons) = 4 ~. (21) 


For any other kind of wood, the resistance to rupture will be in pro¬ 
portion to the respective ultimate crushing-strength, as given in 
Table No. 15. 

35. In the case of the ordinary pole-line, provision must be 
made for two things — wind pressure, and the crushing-weight due 
to snow and ice on the wires. Assuming a wind pressure of 30 lbs. 
per sq. ft., the pressure exerted by the wind on an ordinary 40 ft. 
pole, measuring 7 in. in diameter at the top, and 14 ins. at the 



CONSTRUCTION OF AERIAL CIRCUITS. 


45 


ground level, will be approximately equivalent to a horizontal force 
of about 500 lbs. applied at the top of the pole ; and a difference of 
5 ft. in the length of the pole will make a difference of about 100 lbs. 
in the resultant pressure. 

The pressure per cross-arm carrying 10 wires will be, approxi¬ 
mately, 500 lbs. From such data, the total horizontal force acting 
on the top of the pole can be estimated, and applied in the formulae. 
It must be understood that it is unnecessary to use all the preceding 
formulae in calculating the size of every pole, as, to a great extent, the 
judgment of the designer must be exercised. A pole-line with only 
two or three wires, or a single cross-arm, would need no special pre¬ 
caution against crushing. In a large corner, or terminal pole, wind 
pressure is a comparatively small proportion of the total bending- 
force, and is amply provided for by the factor of safety. In each 
case the controlling destructive force must be provided for, allowing 
the factor of safety to provide for the others. 

The sleet storm, or fall of damp snow, succeeded by a high wind, 
is the worst enemy of the pole-line. There are cases on record of 
ice incrustations on a No. 10 wire accumulating to such an extent as 
to make a continuous cylinder six inches in diameter. The best prac¬ 
tice indicates the advisability of making the poles strong enough to 
withstand all the ordinary attacks of the elements ; if then, under an 
excessive snow load, some of the circuits are ruptured, the repair job 
is an easy one. A broken pole is much more difficult to replace, and 
in the act of falling is apt to drag with it a long section of line, thus 
extending the damage over a large territory. 

36. Guying. — In the open country, there is little or no objection 
to the practice of re-enforcing by means of guy-rods ; but in city lines 
the room occupied in a street by the guys becomes exceedingly 
objectionable, as in many cases the direction of the resultant is such 
as to necessitate a guy situated in such a manner as to interfere with 
traffic. Inasmuch as the method of guying is by far the cheapest 
expedient, it is still resorted to in all cases where it is possible for it 
to be successfully accomplished. 

Various forms of pole-guys are indicated in Fig. 12, illustrating 
also the objectionable forms, such as tying the top of the pole by 
means of a guy, or in placing it directly below the cross-arms. The 
effect of such guying is to cause the pole to bend directly beneath 



4(3 THE ELECTRICAL TRANSMISSION OF ENERGY. 

the arms, and, ultimately, to fail at this point. Probably the most 
valuable form of guy is that known as the “ Y ” guy, consisting in a 
tension member so arranged as to secure the pole directly at the top 
of, and immediately under, the cross-arms. In this way nearly all 
the stress of the line is transferred to the guy, in such a manner as 
not to cause sensible deflection of the pole. When there are more 
than two or three cross-arms, “ Y ” guying should always be adopted. 
Most frequently guys are made either of one or more strands of No. 8 



Fig. 12. Methods of Guying. 


iron wire, or of to f" steel wire strand. The wire strand is to be 
preferred, as it is more flexible, more easily drawn to the proper ten¬ 
sion, and adapts itself more readily to the emergencies of each partic¬ 
ular case. It is also customary, in straight line work, to frequently 
guy the top of each pole to the base of the next succeeding one for 
several poles. By this means the lateral vibration introduced by 
heavy wind storms may, in a great measure, be checked, and fre¬ 
quent instances are on record wherein this method of “head guying,” 
as it is technically termed, has saved a line from destruction. 



























CONSTRUCTION OF AERIAL CIRCUITS. 


47 


37. Anchor Poles. — In city lines, where an abrupt angle occurs, 
or where, for the purpose of entering underground conduits, it is es¬ 
sential to terminate a large and heavy line, it is necessary to provide 



Fig. 13. Structural Iron Anchor Pole. 


a pole of sufficient stiffness to assume the entire tension of all of 
the circuits. The neatest solution of the problem is to design a pole 
of structural iron of sufficient strength to withstand the stresses of 
all of the circuits, in such a manner as to make the pole entirely self- 





























48 


THE ELECTRICAL TRANSMISSION OF ENERGY. 



Fig. 14. Plan and Elevation of Combination Anchor Pole. 
See Table 1G, No. 1. 


Fig. 15. Detail of Main Gay-Rod. 
See Table 1(>, No. 2. 


MAIN PART OF GUYROD. 




















































































































CONSTRUCTION OF AERIAL CIRCUITS. 


49 


sustaining. In ordinary line practice it is customary to stretch each 
wire to a tension of about 150 lbs., while the messenger strands sup¬ 
porting aerial cables usually have a tension of about 8,000 lbs. Thus 
it will be evident that in heavy lines, carrying say from four to five 
cables, and from 80 to 100 wires, the line stresses are by no means 
insignificant quantities, amounting in the above instance to some 



! ... : 


u-42-->4 

I - 33- - 1 l 

| f-A—! i i 

1 ' ''o '0r angiIes 4 V X 

! y I 1 1 If 7 -' UBS PER 

R^rr-7.7?- -f-l 

1 .t 

50 

iH 

8E 

1 , 

|--6—V* h® : 'o°: 

-p-l 

.A. 


! . 


-4-i 

1 \ 


■ |i 



I 

M 

1 

1-6— • 'o 0 *' —y-1 



i 


■■■ -ir.l 

' 

! § 

& 

o; ;oA 

. '■£ 

-1— 

1 i 

l—O— -i c o 1 

! 

W 

-1— 

|V- 


-f-i 

I 

; - i 

u 

r 

! 

1--?—_ -L. _iLi— z±A 

“1- 

, 1 

8 


pp: 


- y— 1 

1 


fVx 4*X >4 

l- 


J -1 

r 

f 

t* 

§ 

Q 


§ 

o ;o 

»! iof 


H— 

i • 

i > 


Fig. 16. Detail of Pole Lattice. See Table 1G, No. 3. 


80,000 lbs. upon the top of the pole. For lines of this magni¬ 
tude, the pole is not less than from 50 to 60 ft. in height, and conse¬ 
quently the bending-moment at the base of the pole is exceedingly 
severe. There is no difficulty in manufacturing a structural iron or 
steel pole, setting the same in a heavy base of concrete, and thus 


























































































































































50 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


attaining the necessary strength. An illustration of such an anchor 
pole will be found in Fig. 13. The only objection to a structure of 
this kind exists in its initial expense, amounting, in the instance 
above cited, to a cost of some $600. As a compromise in the 
matter of expense, the plan has been adopted of constructing a 
composite pole, and anchoring the same by means of a guy-rod. 
The design for such a pole is indicated in Fig. 14, with the essential 
details in Figs. 15, 16, IT, 18, and 19. The pole is made by secur¬ 
ing an appropriate w r ooden spar, about 24" in diameter at the butt, 
and not less than from 10" to 12" at the top, the height of the pole 
conforming to the height of the line. The pole is then provided 
with a frame-work or anchor platform, as shown in plan and eleva¬ 
tion in Fig. 14, by means of which the pole is solidly set into the 
earth. In setting the pole, the anchor platform is set in a direc¬ 
tion away from the longitudinal stress of the line, in order that the 
pole may not fail by overturning, the weight of earth resting upon 
this platform being more than equal to the bending-moment aris¬ 
ing from the line stress. The guy-rod extends from this platform 
to the top of the pole, so arranged as to take through the guy-rod 
branches the horizontal components of the line stress. The details 
of the guy-rod and branches are seen in Figs. 15 and IT. 

The top of the pole consists of a lattice-work of angles, as shown 
in Fig. 16, that are fitted to the top of the pole, three sizes having suf¬ 
ficient range to be readily adapted to all ordinary lines. The lattice- 
work consists of two 3" x T" steel angles latticed together to readily 
fit on to the top of the spar. At appropriate intervals light 3" x 4" 
angles are set, for the purpose of supporting the cross-arms. The lat¬ 
tice-work is secured to the pole by means of the bands shown in Figs. 
18 and 19. At the proper points to balance the line tensions, guy-rod 
bands shown in Fig. 18 are placed, to which branch guy-rods ex¬ 
tending to the main guy-rod, and thence to the anchor platform, 
are attached, by means of swivel clevises, so that any slack in the 
guy-rod may be taken up. A slight consideration of this design 
will show that the lattice-work is amply sufficient to carry, with¬ 
out sensible deflection, and transfer to the two parts of the guy-rod, 
all the horizontal components of the stresses introduced by the lines. 
As a result, the spar is entirely relieved from all bending-moment, 
being subjected solely to the vertical component of the stress in the 


CONSTRUCTION OF AERIAL CIRCUITS. 


51 



See Table 16, No. 4. 



See Table 16, No. 5. 

Fig. 17. Detail of Guy-Rod Branches. 


(-*--M->1 




Fig. 19. Detail of Pole-Bands. See Table 16, No. 7. 


—K->« 


t 


























































































































































































































52 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


guy-rod. Table No. 16 contains full 



dimensions of all the sizes 
necessary for anchor poles 
of this description, capable 
of carrying from four to 
ten cross-arms, and from 
one to four cables. Blanks 
are left for the height of 
the pole, length of guy- 
rods, and size of opening 
in the top and bottom of 
lattice, as these dimen¬ 
sions will vary with each 
pole. The dimension let¬ 
ters in the illustration refer 
to the values to be found 
in the table. Anchor 
poles of this description 
have worked successfully,. 
and may be introduced at 
about one-half the cost of 
the corresponding struc¬ 
tural iron pole. 

The illustration, Fig. 
20, is from a photograph 
of a composite anchor 
pole of this kind, designed 
for 100 wires and 4 cables. 
At the time of the photo¬ 
graph 70 wires were in 
place, but no cables. The 
spar forming the pole was 
a Norway pine stick 70 ft. 
long, 16" at the top, and 
22" at the ground, and set 
10 ft. below the surface. 

The chief criticism to 
be passed is the certainty 
of the early rotting of the pole at or near its base, where the wood 


Fig. 20. Composite Anchor Pole. 




CONSTRUCTION OF AERIAL CIRCUITS. 


53 


Table No. 16. — Dimensions for Combination Anchor Poles. 

No. 1. Data for Anchor Platform. (See Fig. 14.) 


Number of 
Cross-arms. 

Number of 
Cables. 

A 

B 

C 

D 

E 

F 

G 

4 

0 

12' O'' 

20' 0" 

12 77 

8 77 

G 7 0 77 

6 77 

12" 

6 

0 

12' 0" 

20' 0" 

12 77 

8 77 

G 7 0 77 

6 77 

12 77 

8 

0 

13' 0" 

22 ' o // 

12 77 

10 77 

8 7 0 77 

8 77 

12 77 

10 

0 

13 7 0" 

22' 0 // 

12 77 

10 77 

8 7 0 77 

8 77 

12 77 

4 

1 

12' 0 77 

20' 0" 

12 77 

8 77 

G 7 0 77 

6 77 

12" 

6 

1 

13' 0 77 

22 / 0" 

12 // 

10 77 

8 7 0 7 ' 

8 77 

12 77 

8 

1 

13' 0" 

22' 0" 

12 77 

10 77 

8 7 0 77 

8 77 

12 77 

10 

1 

14' 0" 

24 7 0" 

12 77 

12 77 

10 7 0 77 

10 77 

12 77 

4 

2 

13' 0" 

22 7 0 77 

12 if 

10 77 

8 7 0 77 

8 77 

12 77 

6 

2 

13' 0" 

22 7 0 77 

12 77 

10 77 

8 7 0 77 

8 77 

12 77 

8 

2 

14 7 0 77 

24 7 0" 

12 77 

12 77 

10 7 0 77 

10 77 

12 77 

10 

2 

14' 0 77 

24 7 0 77 

12 77 

12 77 

10 7 O' 7 

10 " 

12 77 

4 

3 

13' 0 77 

22 7 0 77 

12 /7 

10 77 

8 7 0 77 

8" 

12 77 

6 

3 

13' 0" 

22 7 0 77 

12 77 

10 77 

8 7 0 77 

8" 

12 77 

8 

3 

14' 0 77 

24 7 0 77 

12 77 

12 77 

10 7 0 77 

10" 

12 77 

10 

3 

14' 0" 

24 7 0" 

12 77 

12 77 

10 7 0 /7 

10" 

12 77 


Table No. 16. 

No. 2. Data for Main Guy-Rod. {See Fig. 15.) 


Number of 
Cross-arms. 

Number of 
Cables. 

A 

B 

C 

D 

E 

4 

0 

If" 

91// 

7 " 

1 1// 
x 2 

3// 

4 

6 

0 

n " 

91// 

Z 2 

7 " 

if 7 

3// 

4 

8 

0 

2 77 

"2 

7 " 

11" 

5" 

10 

0 

2 77 

91// 

-“2 

7 " 

1 17/ 

*2 

7" 

B 

4 

1 

1 7" 

91// 

“2 

7 " 

1 3// 

3// 

4 

6 

1 

2 77 

91// 

7 " 

1 1/7 

r 

8 

1 

2 77 

91// 

"2 

7 " 

1 1/7 
*2 

i" 

10 

1 

91// 

21" 

7 " 

11// 

2 2 

s" 

4 

2 

2 77 

91// 

"5 

7 " 

1 17/ 

*2 

7" 

5 

6 

2 

2 77 

91// 

-2 

7 " 

1 1// 

J 2 

7" 

B 

8 

2 

24" 

4 

91// 

■‘"2 

7 " 

1 1" 

A 2 

7" 

B 

10 

2 

2£ 77 

3 77 

7 \%" 

if 77 

1 " 

4 

3 

2 77 

91// 

"2 

7 " 

1 *" 

7// 

5 

6 

3 

2 77 

91 // 

^2 

7 " 

1 *" 

1" 

8 

3 

91// 

^2 

3 77 

m " 

if 77 

l 77 

10 

3 

2f" 

3£ 77 

9* 77 

2 \" 

1 " 



































54 THE ELECTRICAL TRANSMISSION OF ENERGY. 



6 

£ 

w 

A 

CQ 

<J 

H 


co 

c 

co 


Xfl 

<D 

O 

• rH 

H 


fH 

o 

tM 

c3 

R 


cd 

6 

fc 









































CONSTRUCTION OF AERIAL CIRCUITS. 


55 


Table No. 16. 


No. 4. Data Guy-Rod Branches. (See Fig. 17.) 


Number of 
Cross-arms. 

Number of 
Cables. 

A 

B 

c 

D 

E 

4 

0 

If" 

oi// 

7 " 

14" 

1" 

6 

0 

IS" 

Ol// 

7 " 

if" 

£// 

4 

8 

0 

2 " 

Ol// 

7 " 

H" 

S" 

10 

0 

2 " 

Ol// 

7" 

H" 

S" 

4 

1 

IS" 

91 // 

7" 

if" 

f" 

6 

1 

2 " 

91 // 

7 " 

IS" 

I// 

8 

1 

2 " 

91 // 

"2 

7 " 

H" 

S" 

10 

1 

Ol// 

91 // 

7" 

IS" 

7// 

5 

4 

2 

2 " 

91// 

7 " 

14" 

S" 

6 

2 

2 " 

91 // 

7 " 

IS" 

S" 

8 

2 

2|" 

91 // 

-2 

7 " 

is" 

S" 

10 

2 

Ol// 

3 " 

7 if" 

If/' 

1" 

4 

3 

2 " 

91// 

-2 

7 " 

is" 

S" 

6 

3 

2 " 

24" 

7 " 

is" 

S" 

8 

3 

24" 

3 " 

"if" 

If" 

1 " 

10 

3 

2S" 

34" 

94" 

24" 

1 " 


Table No. 16. 

No. 5. Data for Extension Plates. (See Fig. 17.) 


Number of 
Cross-arms. 

Number of 
Cables. 

A 

B 

C 

D 

E 

F 

G 

8 

0 

f 

34 

7 

54 

2S 

3 

IS 

10 

0 

f 

34 

7 

54 

2S 

3 

IS 

6 

1 

f 

34 

7 

48 

91 

^2 

3 

is 

8 

1 

f 

34 

7 

54 

2S 

3 

IS 

10 

1 

f 

34 

7 

54 

2S 

3 

is 

, 4 

2 

f 

34 

7 

48 

2S 

3 

is 

6 

2 

f 

34 

7 

48 

2S 

3 

IS 

8 

2 

f 

34 

7 

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56 


THE ELECTRICAL TRANS MISS I OH OF ENERGY. 


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CONSTRUCTION OF AERIAL CIRCUITS. 


57 


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58 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


enters the ground. For this defect there is no cure, excepting the 
adoption of the structural iron pole, though a good coat of tar or 
asphalt will give the pole a life of ten or fifteen years. 

38. Setting the poles. — Small and light poles should be set 
some six feet into the ground, and may be planted by simply ex¬ 
cavating a hole a little larger than the butt of the pole, and then 
placing the same in position by lifting the pole bodily, with a 
sufficient gang of men, and dropping it into the hole. Where the 
ground is soft or marshy, or where the stresses brought upon the 
pole by the tension of the lines is excessive, a foundation should 
be formed by excavating a hole of sufficient depth, from four to 
six feet in diameter, and after the pole is planted filling the same 
with a concrete of broken stone, sand, and cement. A good mix¬ 
ture for this purpose may be made of one part of Rosendale cement, 
mixed with three parts of sand, and five parts of broken stone. The 
ingredients should be thoroughly mingled, and carefully moistened 
with about 25 per cent of water, and solidly rammed around the base 
of the pole. After the concreting is complete, the earth may be 
replaced and thoroughly tamped into position. 

39. The “sand-barrel” is often used with success in soft loca¬ 
tions. A stout barrel or cask is placed at the bottom of the excava¬ 
tion, into which the butt of the pole is set. A firm loam, clay, or 
sand, is then packed tightly into the barrel around the pole, thus form¬ 
ing a foundation. In sandy soils the “ temporary sand-barrel ” is a 
most valuable device. This consists of an iron cylinder about the size 
of a very large cask, but split in two parts, and provided with hinges 
and clasps. The cylinder is set at the bottom of the excavation, and 
the pole planted inside of it, and the earth carefully rammed around, 
completely filling the excavation. Then, by means of a fall, the iron 
cylinder is withdrawn from the earth, and, opening the clasps, is 
removed from the pole. For large poles it is customary to cut the 
ground away into a series of steps. The terraces thus made afford 
an opportunity to ease the pole into its position at the bottom of the 
hole ; and then, with a working wagon or derrick and sufficient tackle, 
the pole may gradually be raised to, and sustained in, an upright 
position, while the earth or concrete is tamped around its base. 

40. Insulators. — The number and form of line insulators, to¬ 
gether with the materials proposed for their construction, have been 


CONSTRUCTION OF AERIAL CIRCUITS. 


59 


legion. In this country glass is almost universally used for telegraph 
and telephone work, and for the latter the tendency has been to make 
the insulator as small and light as possible. In England, however, 
the porcelain insulator is the most common, the difference in cl. 
mate fully accounting for the English preference. As an insulating 
material, glass has several disadvantages. It is considerably more 
hygroscopic than porcelain, readily condensing on its surface a film 
moisture which rapidly lowers its insulating qualities. It is very 



Mian ResiSTAMCt 


Porcelain Insulators, 


THE GROOVE 

oouacr. PtrmooAT- patter* 
SCREW JNSnJEATOtt 

zutcrnw uanr urnm. 


'• RGCiiii.AR’* PATTERM 

SCREW GLASS CTMWAATQfL 


Fig. 21. Specimen Insulators. 


brittle, decidedly more so than porcelain or earthenware. While 
blown glass is better in every respect than that which is cast, it is 
so much more expensive that molded insulators are almost univer¬ 
sally used. The great advantage of the glass insulator lies in its 
transparency, which prevents the formation of cocoons under the 
petticoats of the insulator, that have a very marked effect in lowering 
the resistance of lines. Ebonite and india-rubber have been used 
to quite an extent for insulators ; but as they quickly roughen by 
exposure to the weather, and are considerably more expensive, their 















60 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


use has been almost exclusively confined to electric railway work. 
Brown stoneware forms an excellent substance for insulators, as it 
is strong, cheap, and durable, seldom cracks, and its color makes it 
inconspicuous. Thoroughly vitrified porcelain is probably the best 
insulator on the whole, and is used almost exclusively in England 
and on the Continent. The surface resists the formation of film 
moisture, and is easily washed clean by rain. The more common 
forms of line insulators are represented in Fig. 21 (p. 59). 

41. The Value of Insulators. — Many experiments have been 
made to determine the value of poles, cross-arms, and insulators, to 
maintain line insulation. One test made on a telegraph line extend¬ 
ing from New York to Boston, gave a result showing an insulation 
resistance of about 6,000 ohms per mile. 

Some interesting figures derived from tests on cross-arms alone, 
erected in New York city, gave the following data : — 


All four surfaces wet with sponge. 

Soaked one day, left to dry one day, and then wet 

Painted three years before test. 

Same washed. 

Very dry. 11,000 to 

Newly painted. 

Unpainted for many years. 

Same after having been well washed. 

Same after having been well dried. 

Arms and pins together (wet). 


3,120 ohms 
2,680 ohms 
6,150 ohms 
9,166 ohms 
330,000 ohms 
7,214 ohms 
4,300 ohms 
13,653 ohms 
80,000 ohms 
3,686 ohms 


From the same set of experiments the following figures are de¬ 
rived for the insulating power for dirty and soot-covered glass and 
pin insulators. I he tests were made on 40 insulators, thus reore- 

7 X 

senting a mile of line : — 


Dipped in water once. 23,220 ohms 

Dipped in water four times. 56,400 ohms 

New insulators and pins direct from supply dep’t. . 66,600 ohms 

When the same insulators were carefully cleaned, their insulating 
power was raised to about three times the above value. These 
figures give in a striking manner the loss in insulation by exposure 
to smoke and dirt. 

Some more recent experiments have been made by taking 50 of 
each of the typical forms of insulators, mounting them in the ordi- 









CONSTRUCTION OF AERIAL CIRCUITS. 


61 


nary way, and exposing them for some months to the action of the 
weather, the leakage over the insulators being carefully determined 
by the best-known electrical instruments, while a constant meteoro¬ 
logical record was kept of the variations in atmospheric conditions. 
These experiments covered a period of nearly 150 days, observations 
being made at least once a day during the time. About half of the 
observations were made in clear weather, one-fifth in fair weather, 
18 c / 0 in cloudy weather, and 12 ^ in foggy or rainy weather. The 
general results indicate that the greatest losses in insulation occurred 
during foggy or misty weather, when the insulators became coated 
with a thick beady film of moisture. During a heavy rain the in¬ 
sulation was somewhat higher ; and after a storm, when sufficient time 
had elapsed for the drying of the insulator, the resistance of the line 
was considerably improved, owing to the cleaner condition of the 
insulating surface. The open double petticoat insulator was found 
to dry more rapidly than the close single petticoat ; but during actual 
rainfall the loss in insulation of the double petticoat form is greater 
and more rapid than that of the single. In fine weather the large 
sizes of each form indicate parallel results, though the double petti¬ 
coat form gave a much higher resistance than the single form of 
corresponding size. The true value of any form of insulator can 
only be properly computed when a consideration of the actual size 
of the insulating-bell has been eliminated, and attention concentrated 
entirely upon the possible cross-section of conducting material in 
the shape of moisture or dirt which may be deposited upon the 
exterior of the bell. To determine this, it is necessary to ascertain 
the mean circumference of the insulating material, divided by the 
conducting length between the point at which the wire is secured 
and the point of attachment of the insulator to the cross-arm. From 
this, the possible amount of conducting film may be determined by 
multiplying the mean circumference by the distance over the insulat¬ 
ing surface, and evidently a form giving the greatest length in propor¬ 
tion to the mean circumference will have the highest insulating powers. 

42. It is necessary to have the insulators closely and accurately 
fitted to the pins, and to plan the point of attachment of the wire 
as low down as possible, in order to give the smallest leverage upon 
the pin. Many forms of insulators have been recently introduced, 
in which an iron pin is used to secure the insulator to the cross-arm. 


62 


THE ELECTRICAL TRANSMISSION OF ENERGY. 



Fig. 22. Fluid Insulator. 


Practical test, however, shows that the iron pin is frequently weaker 
than the corresponding locust pin, though usually it is strong enough 

to sustain the wire ; such pins fail by bend¬ 
ing, and allowing the insulator to slip off. 
Iron pins possess the very valuable charac¬ 
teristic of not undergoing any essential de¬ 
terioration under weather, and of cutting the 
cross-arm to a much less extent than the 
corresponding wooden pin ; they are defec¬ 
tive, however, in being a much better con¬ 
ductor than the wooden pin, and thereby 
tending to increase the leakage. 

43. Oil Insulators. — The difficulty in 
sustaining at all times high insulation chiefly 
arises in the deterioration of the insulating surface by the deposition 
thereon of conducting films of moisture from rain and fog, or, in the 
cities, by the formation of a coating of greasy dust and smoke. 
Owing to the rapid development of high potential circuits, the neces¬ 
sity has arisen for obtaining the most 
perfect methods of insulation ; and to 
this end insulators containing oil, so 
arranged as to form a barrier to the 
deposit of a conducting film, have been 
proposed, and have been used with 
great success. These contrivances are 
indicated in Fig. 22, from which it is 
obvious that the portion of the insu¬ 
lator underneath the petticoat can read¬ 
ily be filled with a highly insulating 
oleaginous liquid. 

44. Tying and “ Dead-Ending.”— 

To secure the line-wire to the insulator 
would seem a simple matter ; yet to de¬ 
vise a tie that is secure, simple, eco¬ 
nomical, and effective has taxed the 
ingenuity of line men. The standard 
method now in use is shown in Fig, 
the groove of the insulator, on the side away from the pole; a 





Fig. 23. Line-Wire Tier. 


23. The line-wire is laid in 
























CONSTRUCTION OF AERIAL CIRCUITS. 


63 


soft copper tie-wire, one or two gauge numbers smaller than the 
line-wire, is placed in and around the insulator groove, in such a 
manner that one end of the tie-wire shall pass down over the line 
wire, and the other end up over it, as indicated in Fig. 23. The 
fastening is then completed by wrapping the tie-wire continuously 
around the line-wire. Much practice is needed to make this tie 
in the neatest and securest manner, without injury to the surface 
of the hard-drawn copper of the line. The strength of the insu¬ 
lator tie is usually supposed to be, when well made, about one-fourth 
to one-third of the line-wire. When a wire terminates, it must be 
“ dead-ended,” in order to secure it from falling, and transfer the 
tension of the wire to the pole. This is accomplished as shown 
in Fig. 24. The line-wire is carried entirely 
around the groove of the insulator, and either 
wrapped about itself, or fastened with a Mcln- 
tire joint. 

45. Loops. — In order to give service at 
any point on a line, the necessary circuit must 
be carried into the premises of the customer. 

To effect this the line is usually dead-ended 
on the nearest pole, and a loop carried to the 
building to be served. For this purpose 
brackets are necessary ; the best forms for the 
multitude of cases that may arise in practice being indicated in 
Fig. 25, while in Fig. 11 the bracket in place is illustrated. For a 
grounded line, a single pin-bracket is sufficient, for only one wire is 
carried off of the pole. For a metallic circuit, or for a loop in a 
series circuit, a double pin-bracket is required. A favorite form, 
with the method of application, is sufficiently clearly illustrated in 
Fig. 26 to need no additional explanation. Other forms of double 
brackets are seen in Fig. 25. 

46. Stringing 'Wires.—After the poles and insulators are set, 
the erection of the wire is to be undertaken. When there are a very 
few circuits, it is common to mount one or more reels containing 
the necessary wire upon a cart, and then to drive the cart slowly 
along, hoisting the wire up to its appropriate place as fast as the cart 
passes each pole. If a heavy line is in process of construction, the 
work can be greatly expedited by the use of what is termed a 















64 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


“running-board.” A number of reels of wire, usually ten or more, 
are mounted upon spindles, and a piece of wood, practically the same 



Fig. 25. Standard Brackets. 


as a cross-arm, is arranged, to which ten or more wires are attached. 
Horses are then harnessed to the cross-piece, as the running-board 



is termed, and as they “walk away,” dragging the running-board 
after them, the wires are paid out from the reels, and, passing over 










































CONSTRUCTION OF AERIAL CIRCUITS. 


65 


the appropriate cross-arm, may be immediately secured to the 
insulators by linemen stationed for the purpose. After the wire 
upon all the reels has been run out, each wire is pulled up to its 




Fig. 27. Line Dynamometer. 





Fig. 29. The Come-Along in Service. 


appropriate tension by means of a dynamometer, and a small portable 
vise, technically termed a “ come-along,” as illustrated in Figs. 27, 28, 
and 29. 













































66 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


47. Wire Joints. — A legion of methods have been proposed 
for making splices in wire; but for all-round work, where slight 
inequalities in the line are not dej mental, the famous Western 


Union splice, illustrated in Fig. 30, has stood the test of many years’ 
experience, and perhaps can hardly be excelled. For heavy circuits, 
such as electric railway feeds, the splices should be thoroughly 

soldered when made, and 
protected additionally by 
three layers of okonite 

tape thoroughly saturated 
with B. & P. paint. Line 
splices should not be made 
with soldering acid, but 
resin used as a flux, in 

order to guard against the 
possibility of future corro¬ 
sion. In trolley wires, or 
other circuits in which the preservation of continuity is essential, 
without any enlargement of the wire, splicing is most success¬ 
fully made by means of the tubular connector, into which the 
abutting ends of the successive coils may be slipped and brazed. 
This connector is indicated in Fig. 31. For telephone lines of hard- 

drawn copper, the Mclntire splice, as illustrated in Fig. 32, is a 

favorite. This device forms a perfect connector ; is as enduring as 
the wire itself ; is made without the use of soldering, impervious to 



Fig. 30. Western Union Joint 



Fig. 31. Trolley Wire Splice. 


moisture, and is equally strong as a hard-soldered joint. It moreover 
retains the inestimable advantage, especially in the use of hard-drawn 
metal, of retaining in the splice the full strength of the wire. As 
there is no soldering, the joint can be made with fewer tools, in less 
time, and does not anneal the wire. 

48. The Mclntire Splice consists of two tubes drawn side by 
side from one piece of copper, the interior diameter corresponding to 
the external diameter of the wires to be joined. The junction is 
effected by slipping the wires inside the two tubes and then twisting 
























CONSTRUCTION OF AERIAL CIRCUITS. 


67 


the tubes on each other, thus by friction firmly binding the two wires 
together. In big. 82, various sizes, kinds, and applications of the 
Me Intire joint are represented, with the special tools necessary to 
the completion of the joint. Nos. 1, 4, and 6 are completed joints. 
Nos. 2, 8, 5, 7, 10, 12, 13, 14, 15, 16, 19, 20, and 21 are various 
sized connectors fitting wire from No. 16 to No. 0. Nos. 17 and 18 
are connectors used for 
joining two wires of dif¬ 
ferent size. No. 8 indi¬ 
cates two wires thus 
united. No. 11 shows 
the Mclntire joint used 
to take a branch from a 
circuit ; 22, 23, and 24 
are the styles of pliers 
employed to complete 
the splices. 

49. Strength of 
Joints. — The strength 
of wire joints becomes 
an exceedingly important 
item in line construction, 
when it is considered 
that the weights of sleet 
and snow, with which 
aerial construction is fre¬ 
quently loaded in the 
winter time, introduces 
stresses that are danger¬ 
ously near the elastic 
limit of the material. A series of experiments made by the 
Roeblings on copper wire having a strength of 520 lbs., indicate 
the following characteristics for the different forms of making wire 
splices : — 

\ 

Western Union Joint, soldered, average of ten samples, 431 lbs. 83 / 0 of 
breaking strength of wire. 

The Mclntire Joint, average of nine samples, not soldered, 343 lbs. 66 of 
breaking strength of wire. 





Fig. 32. Mclntire Wire Joint. 














































































68 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


Western Union Joint, average of eleven samples, not soldered, 279 lbs. 53 <fc 
of breaking strength of wire. 

Western Union Joint, dipped and soldered with acid flux, 336 lbs. 68^ of 
breaking strength of wire. 

Western Union Joint, dipped and soldered with resin flux, average of ten 
samples, 339 lbs. 66 ^ of breaking strength of wire. 

Western Union Joint, soldered with iron and acid flux, average samples, 490 
lbs. 94 °/c of breaking strength of wire. 

Western Union Joint, soldered with poured solder, resin flux, average of ten 
samples, 443 lbs. 85 ^ of breaking strength of wire. 

Western Union Joints, soldered with poured tallow flux, average of five sam¬ 
ples, 477 lbs. 91 °/c of breaking strength of wire. 

Britannia Joint, two inches solder, average of ten samples, 488 lbs. 94 of 
breaking strength of wire. 


50. The Suspension of Aerial Cables. — Very few of the cables 
that are used for aerial conductors have sufficient mechanical strength 

to be self-supporting over the 
ordinary spans adopted in pole¬ 
line construction, and it is ne¬ 
cessary to arrange some means 
whereby the cable may be sup¬ 
ported at frequent intervals, 
thus relieving it of any tension. 
To this end it is customary to 
run a suspending strand, usu¬ 
ally composed of y steel wire 
rope, between the poles, and 
hang thereto the cable. Methods for supporting the cables are indi¬ 
cated in Figs. 33 and 34, from which it will be seen that the cable is 
sustained by a clip, usually made of zinc, in order to obviate corrosion. 
This clip is passed around the cable, and sometimes secured to a 
hook, which is then attached to the strand of “ messenger wire,” as the 
supporting rope is technically called. In other cases, the clip itself 
forms a double hook, one part of which is devoted to supporting the 
cable, while the other is thrown over the messenger wire. The latter 
expedient is more simple, but not as satisfactory as the one first 
alluded to. It is usual to place the supporting-hooks on the cable at 
a distance of not less than 18" to 24" centers ; as when longer spans 
are attempted, it is found that the lead sheath of the cable fails under 



Fig. 33. Aerial Cable Suspension. 












CONSTRUCTION OF AERIAL CIRCUITS. 


69 


the tension and vibration to which the line is exposed, and, sooner or 
later, will admit moisture. Cable for messenger wire should be a 
good grade of stranded rope, which is as flexible as possible. The 
pole attachment is made by bolting to the pole a piece of angle iron, 
which forms the cable cross-arm. The messenger wire is attached 
to the cross-arm by means of a hook, or even more simply, passed 
directly through holes drilled in the cross-arm, and slotted out in 
such a manner as to prevent the messenger wire escaping. 

Between successive poles the messenger wire should be drawn 
up tautly, in order that, when loaded with the cable, it may not 
present too great a deflection. 

51. The Humming of Wires.—Con¬ 
siderable complaint has arisen from the 
loud humming sound that is occasionally 
produced by aerial lines, upon which the 
wind acts after the fashion of a gigantic 
yEolian harp. Difficulty from this source 
is more frequently experienced upon lines 
which are carried over housetops, for the 
roofs of buildings form a sounding-board 
that is capable of transmitting the sonor¬ 
ous vibrations throughout the entire struc¬ 
ture. Much ingenuity has been expended 
in endeavoring to combat this difficulty with, 

& J 1 Fig. 34. Cable-Hook. 

it is to be regretted, rather poor success. 

The endeavors have been always in the direction of introducing some¬ 
thing between the line and the insulator which would either absorb 
and annihilate the vibrations, or prevent them from being transmitted 
from the insulator and pole to the building. One device consists in 
terminating the line wire a short distance on either side of the insu¬ 
lator, and introducing between the insulator and each side of the 
line a spring having a sufficient stiffness to withstand the tension of 
the line, while, on the other hand, possessing sufficient elasticity 
to absorb and destroy the vibrations produced by the wind. This 
device is exceedingly expensive, not very successful, and introduces 
undesirable complications in the line. 

Another attempt consists in lining the interior of the insulator 
with india-rubber, cork, or a similar substance, placing it between 











70 


THE ELECTRICAL TRANSMISSION OE ENERGY. 





the pin and the insulator. The elasticity of the india-rubber is 
supposed to be sufficient to take out the vibrations from the os¬ 
cillating wire, and prevent them from being transmitted to the 
pole. Unfortunately, any substance of sufficient elasticity to act 
in this manner is hardly strong enough to withstand the severe 
stresses brought upon the insulator by the line; and, sooner or 
later, the insulator becomes loose. 

Another method, indicated in Fig. 35, consists in enveloping the 
wire near the insulator with a piece of india-rubber tubing some 
eight inches in length, which is covered with a piece of sheet lead. 
The enveloped wire is then secured to the insulator, as indicated, by 
means of a second piece of wire, acting as a tie, which is similarly 
enveloped in india-rubber and lead. This device forms a cushion, 

which is fairly successful in ab¬ 
sorbing vibrations, and allows the 
insulator and cross-arm to retain 
their original strength, and is, 
withal, exceedingly economical 
and speedy of application. 

52. The transposition of Tel¬ 
ephone Lines.— Where aerial tel¬ 
ephone lines are of considerable 
extent, and especially where upon • 
the same pole-line other circuits 
are carried, it becomes essential to provide some means of eliminating 
the inductive disturbances that are initiated in the telephonic circuit. 
To accomplish this, the practice has been introduced of changing 
the position of each telephone circuit, with reference to all the other 
circuits, some five or six times in each mile. This is readily done by 
arranging the telephone circuits and the other circuits in such a man¬ 
ner that the circuits occupy respectively the four corners of a square. 
Supposing the corners of the square to be numbered from the upper 
left hand corner in a clock-wise direction, the telephone wires to oc¬ 
cupy 2 and 4 and the other circuits 1 and 3, it is obvious that each half 
of each telephone circuit is contrarily affected by any induction from 
the corresponding halves of the other circuits. By frequently re¬ 
versing the positions, so that in successive intervals the telephone 
circuits occupy the positions 1 and 3 and the other circuits 2 and 4, 



Fig. 35. Anti-Hummer. 










CONSTRUCTION OF AERIAL CIRCUITS. 


71 


while in succeeding intervals the telephone circuits occupy positions 
2 and 4 and the other circuits 1 and 3, the inductive disturbances 
are annulled by reason of the transposition thus introduced The 
general arrangement of such a line is indicated in Fig. 36 ; the 
upper half of the illustration indicating the general appearance of 
the pole-line, while the lower half of the figure shows the placing 
of the circuits at the relative poles where the transpositions are 
effected. 4 his method has been found to be an almost complete 
cure for inductive troubles, and is universally adopted upon all 
telephone lines of magnitude. Its use, however, renders the loca¬ 
tion of line troubles a little more difficult; but, after a short expe¬ 




.2 4, 

jl 3j__ 



d 

.3 3, 

_L 2 2 J_ 

t d 

t 


r n 

\ n 

\ n 

n 


rt POLE 2nd POLE! 3rd POLE 4th POLE 

Fig. 36. Telephone Transposition. 


rience, the linemen become so expert in the detection of trouble 
as to render this difficulty of little magnitude. In order, however, 
to locate a particular line, it becomes necessary to make the trans¬ 
position according to some preconcerted system, which must be 
regularly carried out, or else to mark each wire at each successive 
pole. If transposition occurs at every fourth pole, there would be 
practically ten transpositions in a mile, and consequently, by num¬ 
bering poles, it is easy to trace any particular line. 

The transpositions are readily effected by dead-ending the wire 
at each insulator at which a change is to occur, with a Me Intire 
joint, and then splicing across to the other side of the cross-arm. 









































72 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Some common methods are shown in Fig. 37, the illustration being 
more lucid than any description. 

53. Power Circuits. — Aerial circuits for the distribution of 
large amounts of energy at high potentials are constructed, in gen¬ 
eral, much after the fashion of telephone and telegraph lines, the 
principal differences being in matters of detail. In order to transmit 
large currents, the wire for these circuits must be of correspondingly 
greater cross-section ; and, in view of the greater electrical pressure 
employed, all the wire is entirely covered with insulating material, as 
well as being supported on insulators set on the poles. Though the 

I 



Fig. 37. Transposition Joints. 


individual wires are heavier, power lines as a whole are much lighter 
than telegraph or telephone lines, for it is rare to find more than two 
or three circuits carried on a single pole-line. For this reason the 
poles may be lighter and shorter ; but other details, such as cross- 
arms, insulators, splicing, tying, etc., are precisely the same. On 
account of the greater danger entailed by high potentials, it is well 
to pay special attention to careful insulation, and to secure strong 
and solid construction in every respect. With the exception of rail¬ 
way lines, power circuits are almost always metallic ; indeed, in most 
towns there is legislation against operating high potential circuits on 
grounded lines. 












CONSTRUCTION OF AERIAL CIRCUITS . 


73 


54. Pole-Line Specifications. — The best American practice is 
now constructing pole-lines under specifications, of which the follow¬ 
ing clauses are abstracts of the most important requirements. 

55. Poles. — Standard poles should be of the best quality of 
live, green cedar, butt cuts, squared at both ends. They shall be 
reasonably straight, and well proportioned from top to butt, having 
the bark peeled, and the knots closely trimmed. The poles shall 
be of the following dimensions : — 


MICHIGAN CEDAR. 


Length in 
Feet. 

Minimum 
Circumference 
at Top. 

Minimum 

Circumference 

G ' from Butt. 

20 

18" 

30" 

25 

18" 

33" 

30 

to 

o 

'N 

v. 

36" 

35 

23" 

39" 

40 

23" 

44" 

45 

23" 

47" 

50 

23" 

50" 


CANADIAN CEDAR. 


Minimum 

Minimum 

Length in 

Circumference 

Circumference 

Feet. 

at Top. 

6 ' from Butt. 

20 

18" 

28" 

25 

18" 

30" 

30 

20" 

34" 

35 

21" 

41 " 

40 

21" 

44" 

45 

21" 

47" 

50 

21" 

50" 


A variation in the circumference of the butt of 1" will be allowed, 
but ue above circumference of top must be insisted upon. All poles 
shall be subjected to inspection by a representative of the purchas¬ 
ing company, at points of shipment. The tops of the poles shall be 
carefully roofed, by chamfering the top to equal angles of 45° on 
either side of the pole center. The roof shall be painted with three 
coats of best white lead. Each pole shall be gained with the 
appropriate number of gains to carry the required number of cross- 
arms. The center of the upper gain shall be 10" from the apex of 
the pole roof. Each gain shall be cut square and true with the axis 
of the pole and with all other gains, and shall be cut to accurately fit 
the cross-arms. All gains shall receive two coats of best white 
lead previously to the introduction of the arm. 

56. Guy-Stubs and Anchor-Logs. — The quality of wood shall 
conform to pole requirements. Guy-stubs shall not be less than 
24" in circumference at the top. Anchor-logs shall be 10 in 

diameter and 4 ft. to 8 ft. long. 

57. Cross-Arms. — Cross-arms shall be of thoroughly sound, 
straight-grain timber, and made of Norway pine or Southern pine, 
as specified in particular instances. The arms shall be from 3 feet 




















74 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


to 10 ft. long, 3j" thick, and 4f" deep. They shall be sawn true 
and square, fully up to the dimensions specified. The two 44" sides 
shall be sawn parallel and at right angles to one of the 34' sides. 
The other 34" side shall be chamfered throughout the whole length 
of the arm with the exception of 10" in the center, which shall be 
left square to fit into the gain upon the pole. This chamfering shall 
be done to the radius of a circle about 40" in diameter. All cross- 
arms shall receive two good coats of mineral paint put on with a 
brush. 

58. Iron Steel Fittings. — All iron steel fittings shall be of good 
quality of best refined wrought iron, that would be conformable to 
good bridge specifications, and shall be thoroughly galvanized. 

59. Galvanizing. —All galvanizing may be tested by selecting 
samples, which shall be plunged in a saturated solution of sulphate 
of copper for seventy seconds, and then wiped clean. This process 
will be repeated four times. If, at the end of the fourth trial, the 
sample appears black, the galvanizing will be accepted ; but if any 
deposit of copper is shown, giving an indication that the iron has 
been exposed, the sample will be rejected. 

60. Cross-Arm Braces. — Each cross-arm shall be braced with 
two galvanized iron braces If" wide and 4” thick by 20" to 30' long. 
Each pair of braces shall be screwed to the pole by one galvan¬ 
ized iron carriage-bolt. All braces shall be attached to the cross-arm 
by means of §" galvanized iron carriage-bolts, of sufficient length 
to go through the braces and the arm. A galvanized iron washer 
shall be placed under the head and nut of each bolt. 

61. Cross-Arm Bolts. — Each cross-arm shall be screwed to the 
pole by one §" galvanized iron bolt, extending entirely through the 
arm and pole. Under the head and nut of each bolt a galvanized 
iron washer, not less than 24" in diameter, shall be placed. 

62. Pins. — All pins shall be of the best quality of sound, clear, 
split locust, free from knots and sapwood. The standard pin shall 
be If" in diameter for the shank in the cross-arm, and 4" in length. 
The top of the pin shall be If" in diameter, where it rests upon the 
cross-arm, and then shall be tapered and threaded to fit the insulator 
for which it is intended. The threading and tapering shall be neatly 
and accurately cut, showing the full thread, and shall accurately fit 
the insulator. Each pin shall be secured to the cross-arm by one 


CONSTRUCTION OF ATRIAL CIRCUITS. 


75 


six-penny galvanized iron wire nail driven straight through the 
shank of the pin. 

63. Insulators. — Standard white glass insulators shall be used, 
which shall be sound and strong, free from fins and sharp edges, 
having threaded holes accurately molded and of uniform size. 

64. Guy-Rods. — Anchor guys shall be attached to galvanized 
iron guy-rods. These rods shall be 6 ft. to 8 ft. long, f" in diameter, 
provided with a square galvanized iron washer, in thickness and 
3" square, with a hole for the reception of the rod. 

65. Wire-Rope Fittings. —All wire-rope fittings, such as thim¬ 
bles, guy-clamps, rings, sockets, etc., shall be of first-class quality 
of wire-rope fittings, equivalent, in every respect, to those manu¬ 
factured by the Roebling Company, or Washburn & Moen. 

66. Lightning-Rods. — Every tenth pole shall be supplied with 
a lightning-rod, made of No. 6 galvanized iron wire, carried at least 
one foot above the top of the pole, and secured to the same with heavy 
galvanized steel wire staples, made of No. 4 B. & S. wire. These 
staples shall be 2]" in length. The wire shall be carried down 
the pole, and thoroughly buried in the ground at the base of the 
pole with at least two hand turns. 

67. Guy-Rope. — Guy-rope shall be of a good flexible quality of 
steel rope, preferably of seven-strand. Each strand shall be Siemens- 
Martin steel No. 10 B. & S. wire. The wire shall be cylindrical, free 
from scales, inequalities, and other imperfections. The wire shall be 
capable of elongating 4 per cent in 1 ft. lengths, and shall stand at 
least 15 twists in a length of 6" without breaking. The tensile 
strength of the wire must be at least 4.8 times its weight in pounds 
per mile. The seven strands shall be laid up with a right-hand lay, 
not exceeding 34" in length. The galvanizing of the strands must 
be subjected to the same test as previously specified. Strand-rope 
shall be furnished in coils of such length as to weigh between 150 
and 200 lbs. 

68. Construction Details. — The line shall be located by meas¬ 
uring off, and placing stakes for pole location at distances of one 
130 ft. average. In case of obstacles, the poles should be located 
as near the stakes as possible. In the distribution of the poles, the 
strongest and heaviest poles shall be placed on line corners, while the 
best looking shall be distributed throughout towns and cities, or in 


76 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


front of residences. The length of the pole shall be proportioned to 
the contour of the country, so that the line wire may be strung with¬ 
out abrupt changes in level. On straight lines, all poles shall be set 
in the ground to a depth of 6 ft., unless otherwise particularly speci¬ 
fied. All poles shall be set perpendicularly on straight line work. 
On curves poles should be set with an outward rake. The holes 
shall be dug sufficiently large to admit the butt of the pole without 
hewing; and after the pole is set, the earth shall be returned and 
thoroughly tamped around the base of the pole. Tamping shall be 
done in the proportion of three tampers to one shoveler. Upon 
curves, the poles shall be set to a depth of at least 61 feet. Where 
the soil is particularly soft, artificial pole foundations of concrete or 
timber shall be used. 

69. Placing of Cross-Arms. — On straight line work, the cross- 
arms shall be placed on alternate sides of succeeding poles. On long 
spans, the cross-arms of terminal poles shall be placed opposite the 
long section. At the end of lines, the arms of at least the last two 
poles shall be placed on the side facing the terminal of the line. On 
curves, the cross-arms shall face toward the middle of the curve. 
Long spans of 200 feet shall be head-guyed, and, if possible, side- 
guyed in both directions. 

70. Tying of Wires. — Line-wires shall be tied in the manner 
shown in Fig. 23. On curves, all wires shall be located upon the 
side of the insulator away from the center of the curve. On straight 
lines, all wires to be located on the side of the insulator next the 
pole, excepting the two wires nearest the pole, which are to be on 
the outside of the insulator. 

71. Joints. — The joints shall be made with Mclntire sleeves, 
each having three complete twists. 


CONSTRUCTION OF AERIAL CIRCUITS. 


-77 


CHAPTER III. ( Continued .) 

CONSTRUCTION OF AERIAL CIRCUITS. (Continued.) 

PART II. —ELECTRIC RAILWAY CIRCUITS. 

72. Electric Railway Circuits. — The marvelous extension of 
the electric railway systems, leading, during the past four years, to 
an investment in this country of nearly two hundred millions, has 
caused the development of a special branch of engineering, present¬ 
ing problems in line construction which are unique to this particular 
department of the art. At present, with but very few exceptions, 
the electric railway circuit is an aerial line ; yet it must be able to 
carry very large quantities of electrical energy, at sufficiently high 
potentials to become a source of danger, provided the very best work¬ 
manship and materials are not used. Usually the railway circuit 
consists of a series of conducting wires, called feeds, extending from 
the power station over the route of the railway, from which, at vari¬ 
ous points along the line, energy is supplied to the trolley wire placed 
over the center of the track. Two forms of railway lines are in use, 
respectively designated as “ center , or side pole ,” and “span wire” 
construction, depending upon whether the poles for supporting the 
trolley and feed wires are extended along the street, between, or just 
at one side of the tracks, supporting the trolley wire on brackets, or 
whether they are placed in a double row along the curbs of the street, 
the trolley wire being carried upon span wires extended across the 
street from the tops of opposite poles, while the feeds are carried 
directly on the poles. These methods of construction are indicated 
in Figs. 38, 39, 40, and 41. 

73. The Railway Return Circuit.— With the exception of a 
few of the early double trolley roads, the electric railway line has 
always been a grounded return, the current passing from the station 
through the feed wire to the trolley wire, thence through the car 
motor into the rails, and back to the station through the ground. 
So long as railway systems were small, this practice answered well 


78 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


enough ; but with increasing magnitude, the amounts of energy thus 
discharged into the ground have given rise to very serious and per¬ 
plexing problems. The first noticeable effect was the production of 



Fig. 38. Center Pole Construction. 

earth currents of such importance as to seriously interfere with tele¬ 
phonic and telegraphic service ; then a wide-spread electrolytic action 
made its appearance, affecting in a most serious manner all metallic 
underground structure, such as gas and water pipes, and the lead 
















CONSTRUCTION OF AERIAL CIRCUITS. 


79 


A 


Fig. 39. Side Pole Construction. 



t 






SECTION OF STREET SHOWING 
POLES AND SPAN WIRE. 
















































80 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


sheathes of underground cables ; and lastly, in the larger roads, the 
poor quality of the earth as a conductor makes itself manifest, neces¬ 
sitating a very considerable fall of potential, and consequent waste¬ 
ful expenditure of energy in this part of the circuit. On account of 




Fig. 41. Span Wire Construction with Double Insulation. 


SHORT THICK BOND APPLIED TO “TRAM” OF GIRDER RAIL, 
ALLOWING CONSTANT INSPECTION. 



SHORT THICK BOND APPLIED TO BASE OF EITHER 
GIRDER OR T RAIL. 



30 




SOLID LONG BOND CLEARING THE FISHPLATE IN 
EITHER GIRDER OR T RAIL. 




Fig. 42. Rail Bonds. 


these difficulties, the larger roads are now aiding the ground return 
by re-enforcing it with copper wire “return feeds,” looking in the 
near future to a more or less complete metallic circuit for the railway 
system. 

74. To aid the conductivity of the rails and ground part of the 
circuit, it is customary to “bond” every rail of the track by uniting 

























































































CONSTRUCTION OF AERIAL CIRCUITS. 


81 


the ends of the adjacent rails with a copper wire, as shown in 
Fig. 42 (p. 80). 

The copper wire is attached to the rails by drilling a hole into 
either flange, and firmly riveting the bond into place. Considerable 
difficulty has been experienced with electrolytic action between 
the rail bond and the iron. To avoid this source of difficulty 



Fig. 43. Track and Ground Wire Connection. 


recent practice has shown the advisability of making each bond 
of two or more separate pieces, so that the corrosion and failure of 
one will leave the other still in condition to carry the necessary 
current. Rail bonds should always be so placed as to be open 
to inspection, and careful maintenance should be exercised over them 
constantly. A great deal of difficulty has been experienced in the 


METHOD OF CONNECTING RAILS TO SUPPLEMENTARY WIRE 
BY THE USE OF “CHANNEL PINS.’’ 



Fig. 44. 

use of bonds that are too small for the amount of current discharged 
into the rails. In some cases the bonds have been so heavily loaded 
as to become hot enough to burn their way entirely through the 
sleepers forming the road-bed. It is also customary to unite all the 
rail bonds to a central ground wire extending along between the rails 
of either track, as shown in Figs. 48 and 44. 


























82 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


The ground wire adds to the conductivity of the return circuit, 
but serves a more important office to bridge any gap resulting from 
the accidental destruction of one or more bonds. At frequent inter¬ 
vals, as often as two or three times in every mile, the return wire 
should be thoroughly grounded by attaching it to a long rod or pipe, 
driven down to a permanently moist stratum of earth, or to a ground 
plate buried so deeply as to be always wet. 

75. The result of the most recent investigations indicates, how¬ 
ever, the utter unreliability of placing any. dependence upon the 
earth to form a portion of the return circuit. While in damp 
weather the earth may, under some circumstances, become a valu¬ 
able adjunct, the varying hygrometric condition, sandy soils, and 
imperfect contact between the rails and the ground, are such as to 
reduce the value of this factor practically to zero. It thus becomes 
advisable for every road to provide a complete metallic return circuit, 
of such resistance that, excepting in cases where the cost of produ¬ 
cing energy is abnormally cheap, not more than from 3 to 5 per cent 
of the station output shall be expended in the entire line circuit. 
The tendency of street railway construction is constantly toward the 
use of heavier and larger rails, and a more substantial road-bed, so 
with proper precautions the track may form the return circuit. The 
cross-section of a rail may be fairly accurately estimated by allowing 
one square inch of cross-sectional area to every 10 lbs. of rail weight 
per yard of length; thus, a 50-lb. rail would have a cross-section 
of 5 square inches, and a 90-pound rail, 9 square inches. 

Thus, if W be the weight of the rails per yard in any particular 
track, jy 

— = area in square inches of each rail. 

As the relative electrical conductivities of steel and copper are about 
as one to six, jy 

Wq = the area of a copper conductor that 

would be equal in conducting power to a rail; and for a double-track 
road IV /15 gives the equivalent copper conductor. 

A copper cable equivalent to the rail section of a four-track road 
laid with 50-lb. rails would be 3.3 square inches ; with 60-lb. rails, 
4 square inches ; with TO-lb. rails, 4.6 square inches; with 80-lb. rails, 
5.3 ; and with 90-lb. rails 6 square inches. 




CONSTRUCTION OF AERIAL CIRCUITS. 


83 


1 here are very few electrical railways whose managers are 
sufficiently liberal to provide 6 square inches of cross-sectional 
area in the copper conducting system, though there are many roads 
with ninety-pound rails. Thus, from the previous train of reasoning, 
there is amply sufficient metal provided in the rail sections for the 
return path of the current, at least in anything but the largest and 
longest roads. 

76. The difficulty heretofore encountered with return circuits 
has been almost entirely due to the method of securing continuity 
in the track. When the rails are originally laid, the ordinary fish¬ 
plate joint forms an amply sufficient path for the current; but 
oxidization rapidly sets in, and almost before the road is in opera¬ 
tion the contacts between the plates and the rail are sufficiently 
corroded to interpose a resistance of great magnitude. To overcome 
this, the custom of introducing rail-bonds has arisen. Many roads 
have been constructed by uniting the ends of the rails with No. 6 iron 
wire. In the better forms of construction, the iron wire has been 
replaced by corresponding copper wire, and in addition the ground 
wire has been introduced to aid the rail-bonds. Usually the ordi¬ 
nary bonds have been from two to three feet in length. Now, if the 
continuity of the return circuit be made dependent upon the bond 
connection between the ends of the rail-joints, each mile of track 
will have in the neighborhood of 830 ft. of either No. 4 or No. 6 
iron or copper wire. Taking the most favorable instance of the use 
of No. 4 copper wire, and allowing a double-track road, the resistance 
of the return circuit would be .06572 ohm per mile, an amount 
greatly in excess of that ordinarily allowed in the feed-wire calcu¬ 
lations. A greater difficulty is experienced in the resistance of the 
contact between the rail-bond and the metal of the rail itself. It 
is customary to secure the bonds by drilling the ends of the rail, 
and riveting the bond in place. Unless this work is very carefully 
supervised, the rivets are very rarely tightly driven, and in many 
cases oxidization sets in before the bond is put in place. As 
a result, the resistance of the return circuit may be increased 
to a very large extent over that of the wire employed for the 

bonds. 

77. Some experiments upon the resistance of return circuits on 
the Utica Electric Railway are confirmatory of the advisability of 


84 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


utilizing the track for the return path of the current, indicating that 
the rail section is ample, if proper connections are secured around 
the joints. Of single-track 60-lb. rails, 690 ft. were joined by fish¬ 
plates only, laid on sawed ties, without bonding. T he weather was 
clear, hot, and dry. The resistance was measured, and found to be 
.2006 of an ohm, giving 1.5349 of an ohm per mile of single track, 
and .7675 of an ohm for double track. Measurements made upon 
4,000 ft. of double track with 60-lb. rails, bonded with one No. 3 
copper wire bond and continuous No. 3 copper ground wire, gave 
.025 ohm as the resistance per mile of double track. A measure¬ 
ment upon 3,800 ft. of single-track, 45-lb. T-rails, bonded with No. 4 
galvanized iron wire, gave a resistance of . 0577 ohm per mile of 
double track. 

Calculating the resistance of the bond wires in the track in the 
second test, an amount of .0236 ohm is given, while the measured 
resistance was .0254, a variation of about 10 per cent from the com¬ 
puted amount. In the third case, the measured resistance was .0577 
ohm, and the calculated amount .0556 ohm, giving a difference of 
.0021 ohm per mile. 

78. The solution of the problem, at least for all ordinary cases 
of street railway construction, lies in the entire utilization of all the 
track material as a return circuit, by the proper application of suit¬ 
able conductors, arranged around the joipts of all the rails. 

It is curious that this apparently so simple solution has so long 
been neglected ; but, on further inspection, the apparent simplicity 
resolves itself into a problem of considerable complexity, the diffi¬ 
culty being to secure such a connection between the two rail-ends as 
will be adequate to carry the necessary current, and also will not 
rapidly deteriorate when exposed to the severity of street service. 
In all probability the final and adequate solution will be found in 
some application of electrical welding. At the present time, the 
West End Street Railway Company of Boston is trying the experi¬ 
ment of electrically welding the ends of adjacent rails, so as to make 
their track a single, continuous rail with no breaks, at least for sec¬ 
tions of some thousands of feet in length — the experiment indicat¬ 
ing, contrarily to previously conceived ideas, that expansion devices 
are not necessary in a street railway track. This theory has received 
very strong confirmation from the experiments of Mr. Moxam, at the 


CONSTRUCTION OF AERIAL CIRCUITS. 


85 


Cambria Iron Company ; and, if sustained by additional experience, 
the solution of the problem of rail-bonding, as well as that of track 
construction, will be promptly and completely solved. 

79. A somewhat similar experiment has been tried in Cleveland, 
where a system of railway has been introduced, consisting of 90-lb. 
rails jointed by specially heavy fish-plates, which were riveted solidly 
to each end of the rail. Provided the riveting is done when the rails 
have fairly clean surfaces, it is likely that the joints formed by the 
fish-plates would be electrically sufficient. 

A process has recently been devised that employs the method 
of casting together the consecutive rail-ends. A portable furnace 
weighing about 7,000 lbs., and capable of being drawn by two horses, 
is operated by oil fuel. The furnace has capacity to melt sufficient 
iron to make 150 or 200 rail-joints per day. A mold is placed 
around the rail-ends, and melted iron poured in, that, on solidifying, 
forms a solid block that actually fuses the rail-ends together. No 
better electrical joint could be obtained ; and, if experience shall 
demonstrate the plan to be a mechanical success, another solution 
of the return circuit will be secured. This method is now under 
trial in St. Louis. 

80. Probably, however, it will be some time before the success 
of either of these methods can be demonstrated sufficiently to war¬ 
rant their adoption on large scales. It therefore becomes essential 
to arrange some adequate electrical connection for the ends of the 
rails in existing tracks. To this end, the bond (see Fig. 42) should 
be as short as practicable. Former practice indicated the use of 
bond from 2 to 4 ft. in length ; but there is certainly no adequate 
reason why the bonds should not be reduced to from 6" to 8", as it is 
only essential to have a sufficient length of bond to span across the 
openings between the rails, allowing a small fraction of an inch for 
expansion. There is no reason why heavy copper bonds, thus ar¬ 
ranged, should not be secured to the ends of the rails by some form 
of electrical welding which would make a perfect joint between the 
bond and rail itself — a joint, also, which in the future would never 
be subjected to electrolytic action or corrosion.- If the overhead line 
can be erected previous to the bonding of the track, the operation 
of electric welding becomes exceedingly simple, as it is practicable for 
the power station to furnish all the energy necessary to make the 



86 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


welds. The Boston experiments have indicated that two 90-lb. rails 
can be welded by the application of 100 horse-power for about three 
minutes, while to weld a bond consisting of a 2" by copper strap 
would not require the expenditure of over 20 or 30 horse-power for 
an equivalent length of time. 

81. Where the preceding methods cannot be adopted, the next 
best method consists in forming the bonds of a heavy copper strap, 
some 6" to 8" in length, of at least one-half a square inch of section, 
and having at either end a forged eye, through which a copper bolt, 
not less than than three-quarters of an inch in diameter, may be 
passed. The eyes on the end of the strap and the bolt should be 
thoroughly tinned, and a hole tapped in each rail-end to receive the 
bolt. The bond is applied, and the nuts on either end screwed up 
solidly, so as to pinch the bond tightly between the rail and the head 
of the bolt. The application of the flame of a blow-lamp for a few 
minutes then solders the bond and the bolt together in a solid 
manner. The copper bolt should be sufficiently long to extend 
through the rail for at least one-quarter of an inch, and then 
should be headed over, so that by no possibility it can ever be¬ 
come loosened. 

The thread in the rail should be tapped slightly small, so when 
the copper bolt is screwed home it may be absolutely forced into 
place, the metal of the bolt squeezing itself into the thread cut into 
the rail. By this means a contact of sufficient area between the 
rail and the bond can be obtained, and the joint so thoroughly 
secured by the compression of the two metals, that no future cor¬ 
rosion can take place between the bolt and the rail section. This 
method of bonding is shown in Fig. 45. 

82. A structure of this description will be amply adequate for 
all roads not requiring a line capacity of more than 4” to 6" of 
copper cross-section, for it is evident that the rail area supplies 
sufficient metal section up to this amount. In cases where the 
energy to be distributed requires a line of larger cross-section than 
this, it is essential to re-enforce the rails by such a system of return 
feeders as will add to the rail return a sufficient quantity of copper 
cross-section. These feeds may either be supported upon the regu¬ 
lar line construction of the road, or may be carried between the 
tracks, as in the old form of return ground wire. In either case, 


CONSTRUCTION OF AERIAL CIRCUITS. 


87 


it is essential to frequently connect the return feeds to the rails 
by conductors of adequate size. 

83. In designing the return circuit, care should be taken in 
installations where the rail lines do not pass close to the power 
station, to introduce a sufficient amount of return feeds from the 
station to the rails as shall be fully equal to the cross-section 
of the return circuit as obtained through the rails and return 
feeds. 

84. Electrolytic Action. — The most complete investigation 
upon the electrolytic action of underground currents has been made 



Fig. 45. Improved Rail Bonding. 


by Mr. I. H. Farnham, of the New England Telephone & Telegraph 
Co. 1 Mr. Farnham’s attention was drawn to the matter some three 
years ago, by the appearance of injurious corrosion in the lead 
sheaths of the underground telephone cables. Investigation traced 
the cause of the corrosion directly to the return current in the 
ground from the electrical system of the West End Railway, and 
further showed that the difficulty could be traced to points along the 
cable where the underground currents tended to leave the cable for 
a path of less resistance to the station. At the beginning of these 
investigations, the negative pole of the generating-station was con¬ 
nected to the overhead trolley system, while the opposite pole was 


1 See transactions of American Institute of Electrical Engineers, April, 1894. 































88 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


put to earth. Many volt-meter measurements were made, to obtain 
the difference in potential between the underground cables, water- 
pipes, and gas-pipes, and the surrounding earth, by means of which 
it was possible to map out the entire city of Boston, showing where 
the corrosive action was likely to be expected, thus inclosing an 
area appropriately termed “ Danger District.” It was suggested to 
reverse the poles of the dynamo, placing the positive pole to the 
trolley, and the negative pole to earth. This suggestion was carried 
into effect, and a second set of measurements made, showing that, 
under the new conditions, the amount of the danger district was 
very much decreased, and indicating that the area in which corrosive 
action might be expected was practically confined to the immediate 
neighborhood of the power stations, and thus brought very much more 
under control. It has been pointed out that by restricting the danger 
district, the intensity of electrolytic action may be much increased. 
Such an effect as this is a logical consequence, but the restriction of 
the district to comparatively small areas renders repairs very much 
easier of execution. To protect underground structures within the 
danger district, it has been proposed by Mr. Farnham that large 
copper conductors should be extended from the grounded side of the 
generators, entirely through the district, and should be connected, as 
often as possible, to all metallic structures which are exposed to elec¬ 
trolytic action. This experiment was tried in Boston, subsequent 
volt-meter measurements indicating that the protection thus afforded 
was sensibly complete. 

Mr. Farnham’s investigations further indicated that a very small 
difference in electrical potential was sufficient to initiate the corrosive 
action. 

85. In the discussion of Mr. Farnham’s paper, Prof. D. C. Jack- 
son, of Madison University, gives exceedingly interesting results 
from experiments to determine the minimum amount of electrical 
pressure likely to be injurious, and the chemical effects which are 
produced in the soil through the action of the current. Professor 
Jackson concludes that a difference of potential as small as one- 
thousandth of a volt, constituting mere directive force, may be suffi¬ 
cient to initiate and continue sufficient corrosive action to be injurious, 
provided it extends over a considerable period of time. Professor 
Jackson also says that, in most cases, the action may be considered 


CONSTRUCTION OF AERIAL CIRCUITS. 


89 



Fig. 46. 


Corroded Water-Pipe. 






90 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


to be that of an electrolytic cell with iron electrodes, having an 
electrolyte of the various salts of the alkaline metals, or earths, 
which would be naturally found in the street soils. These alkaline 
salts are electrolyzed by the current, the acid radicals attracted by 
the anode and forming an iron salt, while the metals pass over to the 
cathode, forming with water a hydroxide, liberating hydrogen. The 
ferrous salt thus formed diffuses toward the cathode, while the alka¬ 
line hydroxide, in a similar manner, diffuses toward the anode. 
Where these salts meet in the soil, ferrous hydroxide is precipitated, 

and the original salt re-formed. 



Assuming the correctness of this 
theory, it is evident that the actual 
corrosion is due to an attack by the 
acid radical of the salt in the elec¬ 
trolyte, which is set free by the pas¬ 
sage of the current. 

This investigation still further 
emphasizes the necessity in street 
railway work of providing a metal¬ 
lic return circuit which shall be 
amply sufficient to convey to the 
power-house all the energy required 
to operate the railway system. The 
appearance of corroded water-pipes 
is illustrated in Figs. 46 (p. 87) 
and 47. 

86. Railway Poles. — Nearly 
all of the timber woods have been 
pressed into service for electrical railway construction. Poles of 
pine, cedar, chestnut, cypress, spruce, and tamarack are most fre¬ 
quently in demand. Of these spruce, cypress, and tamarack, and 
occasionally poplar, have been used, particularly in the near locali¬ 
ties in which the various kinds of timber are found native. Spruce 
poles make handsome lines, and are strong and elastic, but have 
a very short life, usually rotting out in from two to three years. 
Cypress and tamarack have great durability, and are largely used in 
the Southern States. Cedar, pine, and chestnut are abundant, and 
in the North poles are usually selected from one of these woods. 


Fig. 47. Corroded Water-Pipe. 





CONSTRUCTION OF AERIAL CIRCUITS. 


91 


White cedar and chestnut are frequently selected, both for cheapness 
and prompt delivery. Pine, whether Michigan, Oregon, Norway, 
Georgia, or North Carolina yellow pine, is usually used for manu¬ 
factured poles. 

By means of a little mill-work, railway poles may be made in a 
wide variety of shape and finish, according to the choice of the de¬ 
signer. Commonly the butt of the pole is left round, while from 
the ground up it is sawed either square or octagonal. A manufac¬ 
tured pole, without question, when carefully made and tastefully 
painted, makes a line of unexceptional appearance. The tops of the 
poles should be carefully chamfered to a neat point, and should be 
thoroughly painted with at least three coats of best white lead and 
oil. In crowded localities, the butts of the poles should always be 
protected by an iron wheel-guard, to prevent injury by collision with 
the wheels of vehicles. 

87. Wooden Poles should be not less than 6" at the top, and at 
least 28 or 30 ft. in length. For center-pole construction the poles 
are set at intervals of from 100 to 150 ft. longitudinally, between the 
rails in case of double track, or just outside of the rail in a single 
track. The poles may be either round or octagonal. They should 
be true, straight, and fully up to the size specified, free from knots 
and shakes, and sound in every respect. Typical railway poles are 
shown in Figs. 48 and 39. 

In setting the poles the base should be thoroughly tarred for a 
distance of 5 or 6 ft., and firmly planted in the earth, special care being 
taken to ram the earth solidly around the pole. Where soft ground 
is encountered, a concrete foundation must be used. 

88. For center-pole construction the poles are supplied with 
brackets as shown in Fig. 38, to which the insulator supporting the 
trolley wire is attached. 

Care should be taken to see that the brackets are sufficiently 
firm and strong, and that they are solidly attached to the pole, as 
frequent accidents have occurred by the fall of the bracket due to 
a blow from a passing trolley. 

89. For span-wire construction, two poles are required for each 
span, one set on either side of the street close to the curb-line. To 
counterbalance the tension of the span, it is customary to set the 
poles with a rake, outward away from the center of the street about 


















































































































































































































































CONSTRUCTION OF AERIAL CIRCUITS. 


93 


18". By this means the tension of the span-wire gradually pulls the 
pole to a straight line. On account of this tension, span-wire con¬ 
struction must be exceedingly solid. Specially good foundations 
must be provided for the poles, and they must be amply stiff to re¬ 
sist the bending-moment due to the span wire. 

90. The span-wire should be made of galvanized iron or steel 
cable about §" to i" in diameter, depending upon whether the line is 
a double or single line. The span-wire should be attached to the 
poles by means of a ratchet shown in Figs. 49, 50, and 51, in order 
that requisite adjustment of tension or location of insulators may at 
any time be made. If rigid economy is desired, the span-wire may 
be fastened by means of an eye-bolt extending through the pole, the 



Fig. 51. Pole Ratchets in Place. 


tension being adjusted by means of the nut on the shank of the bolt. 
Each span-wire should be supplied with two strain insulators, one 
set near to each pole, as a protection against any leakage from the 
trolley wire, as in Fig. 41. The strain insulators are introduced into 
the span-wire by forming eyes in the cable by whipping one end of 
the cable over on itself with annealed copper wire, carefully turning 
in all of the wire ends. It is not advisable to use iron wire for any 
purpose of this kind, as it sooner or later rusts. 

91. Iron Poles. — Iron poles are made either of successive 
lengths of wrought-iron pipe shrunk together at the joints, or of 
some of the various forms of structural iron. A great variety of 
designs may be found in the market, of which the examples in Figs. 
52, 53, 54, and 55 may be considered as typical of the best forms. 



















94 


THE ELECTRICAL TRANSMISSION OE ENERGY. 



X 

X 

* 

X 

s 

t 

\ 

\ 

\ 

* 

\ 

* 


3 


1 


The Lattice-pole, Fig. 52, is an excellent form, and 
may be designed to present a very ornamental appear¬ 
ance in the street. Unfortunately, in the early designs, 



L 




: m 


A 


Si 


=D 






Fig. 52. 

pole. It 


an unwise attempt to produce too 
cheap a pole led to many failures, 
and has caused a prejudice against 
this style that should be unfounded. 
The lattice-pole, being open on all 
sides to inspection and painting, 
presents in this respect an advan¬ 
tage over other designs. The 
Tubular Steel pole, Fig. 53, is 
probably the lightest, stiffest, and 
theoretically the best designed 
is rather the most expensive, and, the inside being inac- 


o 


Fig. 53. Tubular Pole. 




































































































CONSTRUC TION OF AERIAL CIRCUITS. 


95 


F 



Fig. 54. Iron Pipe Poles. 


cessible, the thin metal of the shell is likely to suffer from rust. 
The Iron Pipe pole, Figs. 54 and 55, was the earliest design on the 
market, and is deservedly a favorite, as it may be obtained in any 


























































96 


THE ELECTRICAL TRANSMISSION OF ENERGY. 



desired weight or 
three or four 
nected together 
smaller one. In 
must be paid to 
erly joined, se- 


strength. As usually made, it consists in 
lengths of iron pipe of different sizes con- 
by shrinking each piece over the next 
selecting pipe - poles, particular attention 
the joints, to see that the pieces are prop- 
curely shrunk, and that a sufficient length 


Fig. 55. Pipe-Poles for Center Pole Work. 


of joint (at least 18" to 24") is used, in order- that the respective 
pieces may not loosen under the vibration of the passing trolley. 


























CONSTRUCTION OF A TRIAL CIRCUITS. 


97 


In pipe-poles the joint is the weak point. Iron poles should always 
be set in concrete, as the butt of the pole presents too small a surface 
to secure a permanent bearing against mere earth. 

92. \\ hile the iron pole presents the advantage in appearance, 
and is undoubtedly of greater durability, the metal of which it is 
formed being an excellent conductor, it presents the disadvantage of 
exposing the public to much greater danger from leaky trolley wires. 
The wooden pole is so good an insulator that no accidents have as yet 
been reported from leaks through the pole. With the iron pole, how- 



Fig. 56. Adjustable Iron Pole-Top. 


ever, there are many cases reported where either animals or men 
have received severe shocks from leaky span-wires. 

93. Feed-Wire Insulators, and Pole-Tops.— In addition to 
providing a support for the trolley wire, the railway pole must carry 
feed-wire, guard-wire, lightning arrester, cut-out switches, and elec¬ 
tric light fixtures, and perhaps a lighting circuit. The pole-top 
becomes an important feature in the circuit. Typical pole-tops are 
shown in Figs. 56, 57, 58, and 59. The device illustrated in Fig. 56 
consists of a casting into which any number (up to seven) of iron 
supports may be placed. Each support carries a locust pin to which 







































































98 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


any desired form of insulator may be attached for sustaining the 
feed-wires. 

In Fig. 58 a variety of pole-tops are shown, all of which are 
applicable to the pipe-pole, the designs being arranged to meet the 
usual requirements of street railway work. These tops are made to 
be insulated, if desired, a precaution well worth the slight extra ex¬ 
pense, as leaky trolley wires have already caused sensible damage 

on iron pole lines. 

94. For wooden poles, there 
is no better top than that given 
in Fig. 57, especially where 
heavy feeds are to be carried. 
A cheaper expedient is found 
in bolting a cross-arm on to the 
pole, supplied with wooden pins 
and glass insulators, in a man¬ 
ner precisely similar to that of 
the ordinary telegraph construc¬ 
tion. 

Fig. 59 represents the pole- 
top used in Philadelphia. In 
this case the feeder system is 
underground, the tap running 
up through the center of the 
pole. The span - wire is pro¬ 
vided with a special break in¬ 
sulator close to the pole, and 

Fig. 57. Wooden Pole-Tops. 

provision is made for guard-wire 
and lightning arrester, the whole device being worked out in an 
exceedingly mechanical manner. 

95. Trolley Insulators. — Insulators for supporting trolley wire 
have presented a difficult problem to mechanical inventors, owing to 
the severity of the service to which they are subjected. Insulators 
are usually made by forming a bell of some insulating substance, 
which is hung from the span-wire, or pole-bracket. The trolley wire 
is suspended by a clip inserted into the insulating material forming 
the bell. The general arrangement of standard forms of trolley insu¬ 
lators is indicated in Figs. 60 to 66 inclusive. The attachment of 











































































































































CONSTRUCTION OF AERIAL CIRCUITS. 


99 


Insulated 

Pole-Tops. 



Pole-Tops, 

not 

insulated. 


No. I 5.' 


Fig. 58. 


the trolley wire to the insulator has presented one of the greatest 
difficulties in the problem. In the early forms, the connection be¬ 
tween the trolley 
wire and insulator 
was always accom¬ 
plished by soldering 
the wire to a semi¬ 
circular brass or 
bronze s u p p o r t, 
which was screwed 
to the under side of 
the insulating bell. 

This practice was 
exceedingly objec¬ 
tionable, from the 
fact that it annealed 

the hard-drawn copper used for the trolley wire, and from the 
difficulty which arose in making a change whenever the insulator 

was worn out or de¬ 
stroyed. To obviate 
these defects, a mul¬ 
titude of devices 
arose, whereby the 
trolley wire was in¬ 
serted into a clip 
split through the 
center, clasping the 
trolley wire, which 
was prevented from 
falling out of the clip 
by a screw, or nut, 
which locked the two 
halves of the clip 
holding the wire in 
position. The diffi¬ 
culty of soldering was thus obviated, and by loosening the lock-nut, 
the insulator could at any time be set free from the wire. Such an 
arrangement always presented the difficulty of offering a slight 


CAST IRON CAR 

- FEED-WIRE JUNCTION. 
'COMPOSED OF TWO BRASS 
LUGS BOLTED TOGETHER 


HARD RUBBER SLiEV^ 


CUARO-Wtftf SPAN 



Fig. 59. Pole-Top of Philadelphia Traction Company. 



































































































































100 THE ELECTA’ICAL TRANSMISSION OF ENERGY. 



Fig. 60. Standard Trolley Wire Insulator, with Soldered Ear. fig. 61. Trolley Wire Insulator, with Adjustable Wire Clip. 


































































































































































CONSTRUCTION OF A £ RIAL CIRCUITS. 


101 


impediment to the passage of the trolley, and concentrating the wear 
of the trolley wheel upon the clips in such a manner as to rapidly 
destroy them, allowing the wire to sooner or later fall from the insu¬ 
lator. As these objections are less serious than those presented by 
the method of soldering, the latter design has been adopted. As 
trolley insulators must be adapted to all kinds of line construction, a 
variety of forms must be provided to meet the different methods of 
suspension. Thus, in Figs. 60, 61, and 62, designs are indicated for 
span-wire construction, in which the span-wire is placed through 
ears on top of and around the insulator. In Fig. 63 a form is shown 
that is adapted to angle iron bracket work. In Fig. 64 a bridge and 
mine insulator is indicated, planned to be secured against the under 
side of the overhead roof by means of screws ; while in Fig. 65 a 
double-curve insulator is indicated, the extended ears of which receive 
the pull-offs that hold the curve in position. In Fig. 66 a sectional 
view of the hard rubber trolley insulator is shown, exhibiting con¬ 
struction. The insulator consists of a hard rubber bell, into which 
two threaded bushings of brass are forced, to sustain the trolley wire 
clip and the span-wire ears. The trolley wire split clip is seen in the 
lower part of the illustration. To secure an insulating substance from 
which to form the bells, which should possess sufficient insulating pro¬ 
perties to be safe upon a five hundred volt circuit, and strong enough 
to withstand the blows of the trolley wheel, has presented the greatest 
difficulty in this problem. Glass, porcelain, and india-rubber have been 
tried with but little success. Also various other substances, such as 
mixtures of mica, india-rubber, asbestos, etc., have been experimented 
with. Present practice indicates that a compound of asbestos and 
india-rubber, formed under hydraulic pressure in suitable molds, and 
thoroughly vulcanized, gives the best satisfaction. It is probable, 
however, that the best trolley insulator has yet to be invented. 

96. Railway Line Work.— The railway circuit, for the present 
at least, is necessarily an aerial line. If the trolley wire were 
extended in a single straight line, its erection and maintenance would 
be relatively a simple matter. On the contrary, it must accommo¬ 
date itself to curves of every description, intersect other lines, and 
afford proper methods of switching ; and, at each of its many sup¬ 
ports, it must be thoroughly electrically insulated, with sufficient 
mechanical strength to withstand the severe usage of the trolley 


102 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


/ 




Fig. 63. Angle Iron Bracket Insulator. 
















































CONSTRUCTION OF AERIAL CIRCUITS. 103 



Fig. 64. Bridge and Mine Insulator. 



Fig. 65. Double Curue Insulator. 











































































































































































































104 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


wheel. There are three points in every trolley line deserving of 
special attention, namely, curves , szvitches, and cross-overs. I o sus¬ 
tain the trolley wire at each curve, it is customary to plant special 
guy-poles, to which the entire curve is anchored by means of strain 
insulators or pull-offs ; and a similar method is adopted wherever 
there occurs any change in direction of the trolley wire, as, for 




SECTIONAL view of HARD rubber bell 



Fig. 66. 


example, in the case of turn-outs. The solution of all problems in 
railway line construction may be readily solved by careful application 
of the principle of the parallelogram forces. It is essential to study 
the location of each point on the line where a change in direction 
occurs, and determine the resultant of the forces which act upon the 
trolley wire. As all electric railway work is held in place by means 
of wire guys, all forms of construction are always in tension, and 








CONSTRUCTION OF AERIAL CIRCUITS. 


105 


must be designed to meet this form of stress in every particular. It 
is hardly practicable to give diagrams illustrating all the possible 
forms of wire construction which might be met with. In Figs. 67, 



68, and 69 are given the general methods which are in common use 
on the best roads for curves and turn-outs, in which the location of 
anchor poles and method of staying may be readily seen. To ascer¬ 
tain the correct location for the pull-off pole, or poles, for a curve, 



draw an equilateral triangle, having for its base the cord of the arc 
formed by drawing a line between the tangent points of the curve. 
The last two span-wires should be located at the end of the tan¬ 
gents, which also gives the location of the base of the triangle 





































































106 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


AA'C, Fig. 69. The apex of this triangle gives the best location for 
the pull-off pole at C. If it is inconvenient to locate the pole here, 
it is permissible to move it slightly forward or backward, or a little 
to the right or left, though point C is the only correct location. 
An expedient sometimes adopted for situations of this kind consists 
in making the pull-offs up on an iron ring, and carrying a pendant 
over from the ring back to the pole, which, under these circum¬ 
stances, may be located at any distance along the line CD. If pos¬ 
sible, the guy-poles E and F are advisable. Right and left curves 
may be built, as indicated in Fig. 70, in which A is the point of 


B 



location of the switch, and AC and AC" the two curves extending 
respectively to the right and left. The pull-off pole is located in a 
straight line at B, which is a prolongation of AC', each half of the 
double curve being treated in precisely the same manner as indicated 
for a single curve. 

97. Strain Insulators. — As the trolley wire must be retained 
by tension in its appropriate place along the curve, a form of insula¬ 
tor must be designed which shall sustain a severe lateral pull. Such 
an insulator has already been alluded to in Fig. 65. Another form 
of a similar device is shown in Fig. 71. The trolley wire clip is 
supported by a goose-necked rod, the end of which is protected by 









CONSTRUCTION OF AERIAL CIRCUITS. 


107 


an insulating cover of vulcanized rubber, which is attached to the 
pull-off wiie by means of a bail-shaped swivel, that surrounds the 
head of the goose-neck. Designs for pull-off insulators are as 
numerous as those for trolley insulators, and have met with corre¬ 
sponding success. It is frequently necessary to stay trolley wire 
with lateral guys, which must be carefully insulated; and for this 



Fig. 71. Pull-Over or Curve Bracket. 



purpose it is necessary to insulate the guy from the trolley wire with 
a strain insulator. The strain insulator is always subjected to severe 
tension, often rising to several thousand pounds, and is, further, 
under constant vibration from the passage of the trolley wheel. 
Strain insulators in the past have been defective from weak con¬ 
struction. A good form is indicated in Fig. 72, which consists of a 
strong iron bolt carefully overlaid with vulcanized india-rubber, as 



Fig. 72. The Strain Insulator. 


an insulator. A disk in the center serves the purpose of a break, 
preventing the lodgment of a continuous coating of snow and ice. 
Pull-offs are attached to either end of the guy-wire by means of 
bail-shaped swivels. 

The pull-off wires should be made of f" or steel cable, care¬ 
fully and neatly secured to the insulators and other attachments. 
All guy-poles to which strain insulators are attached must be 
specially heavy, and exceedingly securely set with an extra amount 

































108 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


of outward rake, with especial attention directed to the security of 
foundation. Moreover, insulators, turn-buckles, pull-offs, and other 
fixtures upon which special stress is concentrated, should receive 
particular attention, in view of the severity of service which they 
are called upon to endure. 



98. Anchors. — At the end of every curve and turn-out, and as 
often as every 2500 ft. in the tangents, the trolley line should be 
anchored in both directions by means of ears which are soldered to 
the wire. The object of the anchoring is to sustain the line in 
both directions, so that in case of rupture of the trolley wire, only 



a comparatively short length of line will be pulled down and thrown 
out of service. In default of the provision of anchoring, instances 
have been known when the overhead system of an entire railway fell 
flat to the earth, owing to the rupture of the trolley wire at a single 
point. The method of constructing the anchors is indicated in Figs. 
78 and 74. 























CONSTRUCTION OF AERIAL CIRCUITS. 


109 


A metallic clip, similar in general shape to a trolley line clip, is 
soldered to the wire, from which four guys are extended to the 
nearest lme-poles in such a way as to sustain the longitudinal 
tension of the trolley wire in both directions. These guys must be 
carefully insulated by appropriate strain insulators. Diagrams 73 and 
74 indicate clearly the methods to be adopted in both the case of 
a single- and a double-track road. 

99. Line Sections. — As short circuits are a matter of frequent 
occurrence in street railway work, it is customary to split the trolley 
wire and the feeder system into a number of independent sections, 
by introducing section insulators into various parts of the trolley 



Fig. 75. Section Insulator. 


wire, so that a ground may interrupt the traffic on only a small por¬ 
tion of the line. An approved form of section insulator is shown in 
Fig. 75, and consists of two trolley wire clips which are separated by 
a heavy strain insulator. The ends of two adjacent sections of the 
trolley wire are carried into the metal clips and firmly soldered into 
place, the strain insulator serving as an electrical break between the 
sections, and at the same time ensures mechanical continuity, so that 
the trolley wheel may pass the section insulator without leaving the 
wire. 

100. Switches. — The perfect overhead switch, like the perfect 
trolley insulator, has yet to be devised. All the arrangements so far 
provided for this purpose have been, almost invariably, open to the 
objection that they cause the trolley to run off the wire. Two of 





110 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


the best forms which have yet been placed on the market are shown 
in Figs. 76 and 77. 

From the illustrations, the device is seen to be a metal casting 
furnished with ears for the reception of the trolley wires. On one 
end the switch is provided with a single ear for securing one section 
of the wire, while on the other side the switch is split into two, three, 



Fig. 76. Two-Point Switch. 


or more parts, depending upon the number of diverging lines which 
radiate from the switch. The setting of the switch on the overhead 
line is a matter of considerable care ; and it is only by the most 
skillful placing of the switch that the trolley wheel, under any cir¬ 
cumstances, can be coaxed to remain upon the line. The proper 
location of the switch is shown in Fig. 78, in which the dotted line 



Fig. 77. Three-Point Switch. 


indicates the true path described by the trolley wheel, while the 
heavy central line indicates the correct position of the switch, which 
should be located at the center of the arc described by the trolley. 
Double-track roads never require switches, excepting where two or 
three lines radiate from a single point ; and as such intersections are 
rare, the car conductor can, at these points, be expected to give 
especial attention to keeping the trolley wheel in proper place. In a 









CONSTRUCTION OF AERIAL CIRCUITS. 


Ill 


single track it is necessary to have two switches at every turn-out. 
To avoid the difficulties introduced by switches, it is now custom¬ 
ary to run a double trolley wire over single-track roads. While at 
first this might seem a useless expenditure for wire, it must be recol¬ 
lected that the additional amount of copper employed in a double 
trolley wire may be deducted from the feed-wire ; and, as the trolley 
wire is uninsulated, it is cheaper in proportion than the feeds. The 
trolley insulators are more expensive, but the extra cost entailed 
in this direction is more than compensated by the decreased expense 
in annual maintenance of trolley wheels and switches. 

101. Line Crossings. — Where two different railways intersect 
each other that do not use the same power station, it is necessary to 
so arrange the overhead lines on all crossings as to render the roads 
electrically separate from each other. Each road must have an inde¬ 
pendent trolley right of way, that is electrically entirely distinct from 



that of its neighbor, and yet neither road must place any mechanical 
obstacles that will interfere with the free passage of the other trolley. 
A number of automatic devices have been proposed as solutions of 
the cross-over problem, a typical form employing a light but stiff 
horseshoe-shaped casting suspended by the usual hanger from the 
span wire or bracket. One trolley wire is hung in the upper part of 
the inverted U thus formed, by the usual form of trolley wire insula¬ 
tor, and always runs continuously through the cross-over. The other 
line enters either end of the U-shaped casting, and normally is open 
at this point, thus always affording a free passage for the trolley 
wheel of the first or upper line. To close the lower line a swinging 
bridge is arranged, that, on the approach of a trolley wheel belong¬ 
ing to the lower line, swings into position across the gap in the U, 
providing a complete path for the trolley wheel. While inventions 
of this class are exceedingly ingenious, and are mechanically success- 







112 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


ful under ordinary circumstances, they are likely to fail in stormy 
weather, just at a time when the road is most heavily loaded, and 
their service most in demand. 



Fig. 79. Cross-overs and Switches in Place. 


The illustration, Fig. T9, is a representation of the overhead 
system of two intersecting and two branch railway lines. The loca¬ 
tions of the switches and cross-overs are readily seen. 







CONSTRUCTION OF AERIAL CIRCUITS. 


113 


CHAPTER III. — Continued. 

CONSTRUCTION OF AERIAL CIRCUITS. — Continued. 

• * 

PART III.—LIGHTNING ARRESTERS. 

102. Lightning Guards and Strong Current Arresters. — Aerial 
circuits are constantly exposed to the incursion of abnormal amounts 
of electrical energy, either from atmospheric sources, or from acci¬ 
dental contact with other systems. As far as the line is concerned, 
about the only damage that usually happens is to burn off one or 
more wires. Unfortunately, however, extraneous electricity is not so 
easily satisfied, but almost invariably finds way into the terminal sta¬ 
tion, and there creates havoc among the apparatus or machinery. 
As long as the problem to be solved was the protection of telephone 
and telegraph circuits from atmospheric electricity, lightning protec¬ 
tors usually consisted of two serrated plates, one being in series with 
the line, while the other was set close to, but not touching, the first 
plate, and connected to the ground. Protectors of this description 
were based upon the theory that the high potential of the lightning 
flash would jump the small air-gap between the serrated plates, 
rather than go through the remainder of the circuit in order to get 
to earth. While these devices did fairly good work, and undoubt¬ 
edly obviated a large amount of damage, it soon became evident that 
they were not universally successful. Recent investigations show 
that lightning discharges consist of a great number of very rapid elec¬ 
trical oscillations, and that the impedance of almost any circuit is 
sufficient to cause currents of such high frequency to spit off, and 
to seek return paths in all directions. In order to increase the im¬ 
pedance of circuits which it is desired to protect, it is customary to 
introduce impedance coils that consist of an iron core surrounded 
with a few turns of copper wire, so planned as to present little or no 
ohmic resistance, the iron core being of sufficient size that the nor¬ 
mal current flowing through the coils shall excite but a very small 
degree of magnetism, the idea being that the foreign current will 


114 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


cause a great number of magnetic lines to be added to the circuit, 
thereby increasing enormously its. inductance, and opposing a large 
amount of impedance. Lightning arresters of this description, con¬ 
sisting of a number of coils in series, each one fitted with a corre¬ 
sponding spark-gap, have been used with great success by Dr. 
Lodge, and are employed for the protection of sensitive and delicate 
instruments used in submarine cable work. 

103. The introduction of circuits carrying large currents at high 
potentials gave rise to an additional factor in the problem of protec¬ 
tion, from the fact that while the spark-gap operated to divert to 
earth a lightning flash or foreign current, an initial discharge occur¬ 
ring between the serrated plates was suffi¬ 
cient to establish an arc, which was thereafter 
maintained by the heavy current, until the 
serrated plates were consumed and the light¬ 
ning guard destroyed. Therefore it became 
necessary to introduce some additional appara¬ 
tus which should break or interrupt the arc 
thus started. To accomplish this end, inven¬ 
tors have labored in five different directions, 
the results of which have been embodied in 
various mechanical devices, the following being 
representative illustrations of each plan. 

104. (1) High Resistance Arresters have 
been made, consisting of a number of thin 
metal plates, each separated from the other 
by means of a sheet of mica or other infusible insulating substance. 
The line is connected to the top plate, while the bottom plate is in 
electrical communication with the ground. On the occurrence of a 
lightning flash the enormous electromotive force of the discharge is 
supposed to enable the current to find its way over all of the insulat¬ 
ing gaps and to ground, while the gaps introduce sufficient resistance 
to prevent the continuance of an arc after the atmospheric discharge 
has ceased. This form of lightning arrester is exemplified in Fig. 
80. From its simplicity this invention has received quite wide 
introduction. 

The life of this arrester, however, is short, owing to the fact that 
at each discharge globules of molten metal are likely to form on the 



Fig. 80. High Resistance 
Arrester. 


































CONSTRUCTION OF AERIAL CIRCUITS. 


115 


edges of the disks that bridge across the insulating gaps, and in a 
short time completely eliminate them, thus short-circuiting the 
line to earth. 

105. (2) The Magnetic 

Blow-Out Arrester. — This 
apparatus, invented by the 
Thomson Houston Co., is 
represented in Fig. 81. It 
consists of a coil of wire, in 
series with the line and appa¬ 
ratus to be protected forming 
the helix of an electro-magnet, 
between the poles of which are 
placed two cam-shaped pieces 
of metal, one being connected 
to the line and the other to 
earth, and which are separated 
by a small air-gap. Under an 
atmospheric discharge the 
electro-magnet presents suffi- 



Fig. 81. Magnetic Blow-Cut Arrester. 


cient impedance to divert the flash, and make it cross the air-gap 
between the cam-shaped pieces of metal, while the arc which is thus 



Fig. 82. Mechanical Magnet Arrester. 


formed, being in a strong magnetic field, is extinguished by the action 
of the electro-magnet. For central station work this has proved an 
efficient and valuable instrument. 

























































































































































































































































































11G THE ELECTRICAL TRANSMISSION OE ENERGY. 

106. (3) The Mechanical Magnet Arrester. — A third form of 
lightning arrester is indicated in Fig. 82 (see p. 115), in which the 
extinguishment of the arc is effected by electro-mechanical means. 

This device consists of a rectangular block of slate, upon which 
are set two holders carrying two pieces of electric light carbon, 
A A. In the center of the block is an electro-magnet, the armature 
of which forms a lever, carrying at each end two similar pieces of 
carbon, that, in their normal positon, form two small air-gaps, in 
connection with the previous holders. One of the holders is con¬ 
nected to the line and the other to earth. On the passage of an 
atmospheric discharge the flash is shunted, partly through the elec¬ 
tro-magnet, which is thereby excited, and partly through the two air- 




Traftey 


Fig. 83. Air Expansion Arrester. 


gaps to earth. On the excitement of the electro-magnet, it attracts 
its armature, causing the lever to spring away, carrying its carbon 
ends away from the holders, thus increasing the gap between the 
holders and the lever to such an extent as to break the arc which 
has been formed. As soon as the arc is extinguished, the current 
ceases to flow through the electro-magnet, and the lever swings back 
to its normal position, so that the arrester is self-setting. 

107. (4) Air Expansion Arrester. — A lightning arrester intro¬ 
duced by the Westinghouse Company is indicated in Fig. 83. 

This device consists of a slate box carrying a swinging arm H, 
supplied at its end with a semicircular rod of carbon B. Inside of 
the box there are two carbon points AA', placed so as to closely 




































CONSTRUCTION OF AERIAL CIRCUITS. 


117 


approach the carbon arc H. It will also be noticed that the box is 
divided into two parts by the partition 00'. The points A and A' 
are connected to earth, while the line is attached to the insulated 
center pivot K. \\ hen a discharge takes place, the current finds its 
way through the metal arm H into the semicircular carbon rod B, 
jumps the air-gap O into the carbon point A, and thence to earth. 
An arc is consequently formed at the point O, which instantly heats 
and expands the air in the compartment of the box in which the 
discharge takes place. I his expansion of the air is sufficiently great 



to blow the carbon rod out of the box ; and as it swings around on 
the pivot K, the lightning arrester resets itself automatically by 
entering the compartment on the other side of the partition, and 
taking up its position in proximity to the other point A'. 

Carbon points are used in the lightning arresters because they 
are infusible, are fairly good conductors, and may be easily replaced 
when worn. 

108. (5) Non-Arcing Metal Arresters. — While experimenting 
on the subject of lightning arresters, Mr. Wurtz made the singular 
discovery that metals of a certain chemical group would not allow of 
























































































































118 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


the formation or continuation of an arc. This singular and fortunate 
discovery has led to the invention of a lightning arrester made of 
non-arcing metals, as shown in Fig. 84 (see p. 117). 

From the illustration, it will be seen that upon a slate base there 
are placed seven metallic cylinders, the exterior cylinders on each 
side of the center being connected with the line, while the central 
cylinder is grounded, the intermediate cylinders forming a series 
of air-gaps. The cylinders are separated by about the thirty-second 
of an inch. When a flash takes place, the discharge crosses the air- 
gaps, seeking the center cylinder, and thence to earth. Mr. Wurtz’s 
discovery lies in the fact that certain metals of the cadmium group 
do not permit the continuance of an arc, probably due to the fact 
that when the spark first crosses the gaps it volatilizes and oxidizes 



G 


Fig. 85. Diagram of the Wurtz Condenser Arrester. 




a certain amount of the metal, and extinguishes itself by interposing 
a non-conducting medium between the two surfaces. The lightning 
arrester here described is chiefly valuable in alternating current work, 
as it is found that, with continuous current machines, the arc is not 
entirely extinguished, though it is rendered comparatively harmless. 

109. Discriminating Arresters. — In a recent paper before the 
American Institute of Electrical Engineers, Mr. A. J. Wurtz illustrates 
two new forms of what he terms “discriminating lightning arresters.” 1 

The invention of a non-arcing lightning arrester, by Mr. Wurtz, 
seemed to present an exceedingly satisfactory method of protection 
for alternating current circuits. On continuous current circuits, 
however, this lightning arrester does not entirely extinguish the arc, 


1 See transactions of American Institute of Electrical Engineers, May, 1894. 





































CONSTRUCTION OF AERIAL CIRCUITS. 


119 


although it renders it comparatively harmless and quiet. Continuing 
experiments, Mr. Wurtz proposed the device of a condenser lightning 
arrester particularly adapted to continuous current circuits. This 
device may be illustrated by diagram, Fig. 85, indicating the 
method in which the experiments were carried out. A 500-volt 
continuous current generator is represented at A, connected to an 
external circuit LG. Across the circuit a condenser K, having a 
high resistance shunt S, is placed — this high resistance shunt being 
constructed of a heavy lead-pencil mark upon a sheet of glass ; at 
C a spark-gap is arranged. The condenser serves the purpose of 



furnishing sufficient capacity in the line to absorb the violent oscil¬ 
lations set up by lightning discharges, while the high resistance 
shunt S serves the purpose of constantly keeping the condenser 
discharged to earth, thus keeping it from ever becoming overloaded, 
the high resistance of the shunt preventing the dynamo from arcing 
through it. Under these circumstances, the most violent disruptive 
discharges at B, through C to G, fail to injure in any particular 
either the condenser or the generator, and the arc at C is not main¬ 
tained. This device has been put into practical operation in some 
of the Western electrical railways, and has given most gratifying 
results. 





120 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


110. A continued study of the subject led to the invention 
of a still more simple non-arcing constant current arrester, which for 
simplicity and cheapness, as well as of effectiveness in action, seems 
to be almost unsurpassable. This arrester is illustrated in Fig. 86, 
and consists of two blocks of marble about 8" wide, 3^" long, and 
1" thick. In the lower block two brass electrodes 1" wide are laid 
and finished flush with the surface, the distance between the ends 
of the electrodes being about i". This space is occupied by a series 
of blocks of lignum vitae, which are thoroughly charred, or contain 
a series of charred grooves about -fa" wide, and 3 V' deep. The outer 
marble block is intended simply to act as a cover, and to protect the 
apparatus from injury. The charred wood seems to form a conduct¬ 
ing path of so high resistance as to prevent the dynamo voltage from 
crossing it, and yet forms a conductor of sensibly low resistance 
to the high potential of the lightning flash. Furthermore, the 
carbon being essentially non-volatile, even under the temperature 
of the electric spark, no adequate metallic vapors are formed to 
sustain the arc that is initiated by the flash. As a result, the 
electrical oscillations set up in the conducting circuit by an electric 
storm, pass with comparative readiness across the carbon blocks, 
which are of sufficiently high resistance to extinguish and prevent 
any dynamo arc. During the past summer these lightning arresters 
have been given a very successful exhaustive trial on several of the 
Western electrical railways particularly subject to electric storms. 

111. Automatic Cut-Outs. — Both circuits and central station 
machinery are exposed to danger from overloading. A demand may 
be made by the line that is sufficient to injure the station machinery ; 
or, conversely, some disarrangement of the station may expose the 
line to damage from an overload of current. To obviate difficulty 
from this cause, a great variety of inventions have been proposed, 
designed to effect the automatic opening of the circuit to be pro¬ 
tected when a current greater than the normal amount flows into 
the line. The most notable and widely extended of these devices 
is the simple fuse. A block of insulating material is interposed in 
the circuit, upon which a fine wire or strip of some easily fusible 
metal, such as lead or tin, or some of the lead-tin alloys, is extended, 
forming a part of the circuit. The size of this strip is so calculated 
that, upon any sensible increase of current in the circuit, the strip 


CONSTRUCTION OF AERIAL CIRCUITS. 


121 


will melt and open the circuit. Experience, however, has shown 
that the melting-point of fuses is difficult to determine with sufficient 
accuracy, on the one hand, to afford a protection, and, on the other, 
not to open the circuit too frequently upon slight increase of current. 
It is also found that considerable time is required to replace a fuse 
when it is burned, making a long interruption of service. Blocks, 
carrying two or more fuses, which may be rapidly plugged in and out 



Circuit Breaker Closed. Fig. 87. Circuit Breaker Open. 


of the circuit, form a partial solution of this part of the problem. 
But the fuse-block cannot be considered all that is desired for a 
protecting apparatus. Automatic devices have been produced to 
obviate the defects of the fuse-blocks, with more or less success, a 
typical form of which is shown in Fig. 87. 

This apparatus consists of an electro-magnetic clutch, forming a 
part of a spring switch so arranged that, when the current in the line 
increases over the normal amount, the increased magnetism of the 










































































































































































































































































122 THE ELECTRICAL TRANSMISSION OF ENERGY. 

electro-magnet will be sufficient to release the catch holding the 
switch in position, and the powerful spring, to which the blades 
of the switch are attached, will be able to act, and, throwing the 
switch out of gear, open the circuit. In order to obviate the de¬ 
structive arc which would naturally form between the blades of the 
switch, two carbon rods are arranged, FF', to play along two carbon 
plates G and G'. The arc which is formed occurs simply between 



Fig. 88. Cwitchboard Protector. 


3 



Fig. 89. Cable Protector. 


the carbon, which can be readily replaced as fast as used. Auto¬ 
matic cut-outs of this kind can be adjusted to an exceedingly small 
variation of current, and may be reset so quickly as to cause little or 
no interruption to the circuit. For all railway work, apparatus of 
this kind is absolutely essential. 

112. Cable and Switchboard Protectors. — Underground cables 
have been severe sufferers from incursive currents of sufficient mag¬ 
nitude to fuse the lead covering of the cable and entirely destroy 
them. To afford a protection, a special fuse device, indicated in 
Fig. 89, has been put in service upon cable-heads forming the 
junction between aerial lines and underground systems. The illus- 











































































CONSTRUCTION OF AERIAL CIRCUITS. 


123 


tration shows a single protector, the entire cable being secured by 
arranging a sufficient number of these protectors, one after another, 
to correspond to the number of wires. The protector consists of 
a tube of vulcanized fiber or india-rubber about 6" in length ; the 
ends of the tube carry metallic bushings, one end being attached 
to a spring A, to which the aerial line is connected, while the other 
end is secured to a metallic block B, in electrical connection with 
the wire in the cable. Through the insulating-tube extends a lead 
fuse arranged to blow at any desired current, forming the only con¬ 
nection between the cable and aerial line. As the end B is sealed, 
while the end A is open to the atmosphere, the blowing of the fuse 
causes a disruptive charge, forcing the products of the fusion of the 
lead wire violently out into the air, thus extinguishing the arc. Ex¬ 
perience with this protector has been gratifying, though as yet it 
is of but limited extent. 

113. Switchboard Arresters. — At the switchboard end of Tele¬ 
graph and Telephone lines, an endeavor has been made to combine a 
lightning arrester with a sneak current protector, by means of the 
device indicated in Fig. 88. 

The contrivance consists of two parts, — a lightning arrester 
made of two carbon plates, seen at A A, and a sneak current 
arrester in the form of a fusible heat-coil at B. One-half of each 
pair of cable wires enters the terminal C, the other the terminal D. 
The wire D passes through spring F to spring G, and thence to the 
switchboard through F. Spring F, however, is in contact with 
two peculiarly shaped carbon plates. These carbon plates are 
shown in detail at H. The plates consist of two little blocks of 
carbon about V' thick, one having a groove in the top into which 
the spring fits. The lower carbon rests upon a metal plate that is 
thoroughly grounded, and the carbon in addition has a small central 
concavity filled with a drop of fusible metal. The two carbons are 
separated by a sheet of mica about aW' in thickness, cut out in 
such a manner as to bring the drop of fusible metal in the lower 
carbon almost in contact with the upper carbon plate. A flash of 
lightning entering D is supposed to follow through spring F to the 
carbon plate, and then to jump the small air-gap presented by the 
film of mica, and go to ground through the lower carbon plate. In 
case the flash should be of sufficient intensity to cause a sensible 


124 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


amount of heat, the drop of fusible metal is melted, and at the same 
time sufficient expansion is initiated to short-circuit the two carbon 
plates across the film of mica, thus dead-grounding the entire com¬ 
bination, and affording protection to the switchboard. 

114. In the case of a sneak current, there might be insufficient 
voltage to cause the discharge to leap the ^Jo" of the mica gap, and 
yet a sufficient quantity of current might be presented to injure the 
switchboard. To avoid this, the heat-coil B is introduced in the cir¬ 
cuit between the springs G and F. This heat-coil consists of a fine 
German silver wire wrapped around a small metal plug, which is held 
in its place by a drop of solder having an exceedingly low melting- 
point. The heat-coil is individually shown at H, where the project¬ 
ing metal point may be readily distinguished. A close inspection of 
the cut indicates that the heat-coil rests between the springs F and 
G, while the point projects through spring F, and rests upon a thin 
spring directly underneath spring F, over the ground plate, and yet 
not in contact with the same. Upon the passage through the heat, 
coil of a current of sensible magnitude, in the neighborhood of 
amperes, there is sufficient heat evolved in the fine German silver 
wire to melt the drop of solder, thus allowing the tension of spring G 
to force the pin through the coil, down upon the auxiliary spring, 
pressing this spring to metallic contact with the ground plate, thus 
dead-grounding the system, short-circuiting the switchboard, and pre¬ 
venting the sneak current from injuring the apparatus. Inasmuch 
as the heat-coils are found to ground the line with the passage of T y% 
amperes, and as most telephonic and telegraphic apparatus can, for 
some time, resist a current of 4 ampere, it seems that this device 
furnishes fairly reasonable protection to switchboard apparatus. The 
other half of the cable pair, entering by the terminal C, passes, by 
means of an insulated bolt, through the iron frame on which the 
apparatus is placed, to a second set of springs, heat-coils, and carbon 
plates, arranged to duplicate the first set, and passes to the switch¬ 
board by E'. Thus both wires of a metallic line are protected. 


INSURANCE REGULATIONS FOR CIRCUITS. 


125 


APPENDIX TO CHAPTER III. 

INSURANCE REGULATIONS FOR THE INSTALLATION OF CIRCUITS. 

The following extracts from the National Electrical Code give a 
consensus of the best expert opinion as to precautions desirable in 
the construction of electric circuits. 

115. GENERAL ARRANGEMENT OF RULES. 

Class A. — Central Stations, dynamo, motor, storage-battery rooms, and 
transformer sub-stations, Rules 1 to 11.* 

Class B. — Outside Work, Rules 12 to 13. 

Class C.— Inside Work, Rules 14 to 39. 

a. General Instructions, all systems and voltages, Rules 14 to 17. 

b. Constant-Current System, Rules 18 to 20. 

c. Constant-Potential Systems. 

1. All voltages, Rules 21 to 23. 

2. Voltages not over 300, Rules 24 to 31. 

3. Voltages between 300 and 3,000, Rules 32 to 37. 

4. Voltages over 3,000, Rules 38 and 39. 

Class D. — Specifications for Wires and Fittings, Rules 40 to 55. 

Class E. — Miscellaneous, Rules 5G to 59. 

Class F. — Marine Wiring, Rules GO to 72. 

116. Class A. 1. Generators Must Be — 

a. Located in a dry place. 

b. Never placed where hazardous processes are carried on or where exposed 

to inflammable gases or flyings of combustible material. 

c. Insulated upon floors or base-frames kept filled to prevent the absorption 

of moisture, and must be kept clean and dry. If base-frame insulation 
is impractical, the metal frame should be permanently and thoroughly 
grounded. If frame insulation is impractical, the machine should be 
surrounded with insulated platforms to prevent injury to operators. 

d. Protected by approved safety fuses. 

e. Supplied with waterproof covers when not in use. 

f Supplied with plate, stating maker, capacity in volts, amperes, and normal 
speed, R. P. M. 

117. 2. Conductors, Extending from Generators to Switchboards or 

Other Instruments and Thence to Outside Lines, Must — 

a. Be in plain sight or readily accessible. 

b. Have approved insulation as called for by rules in Class C. In central 

stations exposed circuits must have a heavy braided non-combustible 
outside covering. Bus bars may be made of bare metal. 

c. Be rigidly placed. 

d. In all other respects be installed as required by rules in Class C. 

V 

118. 3. Switchboards. 

a. Must be so placed as to prevent danger of communicating fire to adjacent 
material. 


126 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


b. Must be made of non-combustible material or of hard wood in skeleton 

form, filled to prevent absorption of moisture. 

c. Must be accessible from all sides when wired from the back, but may be 

placed against a non-combustible wall when wired on the face. 

d. Must be kept free from moisture. 

e. Bus bars must be equipped in accordance with Rules for conductors. 

4 . Resistance Boxes and Equalizers. 

a. Should be placed upon switchboard, or, if not, placed at least one foot 
from all combustible material, and protected by non-inflammable, non- 
absorptive, insulating material. 

5 . Lightning-Arresters Must Be — 

a. Attached to each s'ide of every overhead circuit. 

b. Located in accessible places, away from combustible materials, and as near 

as possible to the point where the wires enter the building. Station- 
arresters should be placed upon the switchboard. Kinks, coils, sharp 
bends in wires, between the arresters and outside lines, must be avoided. 

c. Provided with a good, permanent ground by conductors equal in conduc¬ 

tivity to a No. 6 B. & S. copper wire. Ground conductors should be 
run in straight lines from the arresters, and never attached to gas-pipes. 
Choke-coils can be introduced between the arresters and the dynamos. 
Ground wires should not be inclosed in iron pipes. 

119. 6. Care and Attendance. 

a. Competent employees must be provided for all dynamo machinery. 

b. Oily waste must be kept in metal waste-cans, with legs raising the bottoms 

at least 3 inches from the floor, and with self-closing covers ; remove 

waste daily. 7 Testing. 

a. All circuits must be provided with reliable, preferably automatic ground 

detectors, never grounded to gas-pipes within buildings, and — 

b. Where automatic detectors are not practicable, tested daily. 

c. Data from tests must be preserved for Inspection Department. 

120. 8. Motors. 

a. The general provisions for generators, a to f inclusive, apply to motors. 

b. Must be wired with the same precautions required by rules in Class C. 

c. The motor and its resistance-box must be protected by cut-out and con¬ 

trolled by switch, plainly indicating whether current is on or off. For 
one-quarter horse-power, or smaller motors on low-tension circuits, a 
single-pole switch will suffice. The switch and rheostat must be located 
within sight of the motor. 

d. Rheostat or starting boxes must conform to Rule 4. 

e. Must not be run in series-multiple or multiple-series. 

f. Must be provided with waterproof cover when not in use. 

g. Electric ceiling-fans must be hung from insulated supports. 

121. 9 . Railway Power Plants. 

a. Each feed-wire before it leaves the station must be equipped with an auto¬ 
matic circuit-breaker, mounted upon fireproof base in full view and easy 
reach of the attendants. 

122 . 10 . Storage or Primary Battery Installations. 

a. When current for light or power is taken from primary or secondary bat¬ 
teries, the same general regulations must be observed as applied to 


INSURANCE REGULATIONS EOR CIRCUITS. 


127 


similar apparatus fed from generators developing the same difference of 
potential. 

b. Storage-battery rooms must be thoroughly ventilated. 

c. Secondary batteries must be insulated. 

d. Metal connections liable to corrosion must be avoided. 

123. 11. Transformers — 

Must be so placed that the burning of the coils or boiling over of the insulat¬ 
ing-oil can do no harm. 

124. Class B. Outside Work. 12. Wires. 

a. Service-wires must have approved rubber insulation. Line-wires must 

have approved weatherproof or rubber insulation. Tie-wires must have 
an insulation equal to that of the conductors they confine. 

b. Must be so placed that moisture cannot form a cross between them, not 

less than one foot apart, and not in contact with any substance other 
than their insulating supports. Service-blocks must be covered with 
two coats of waterproof paint. 

c. Must be at least seven feet above the highest point of flat roofs, and at 

least one foot above the ridge of pitched roofs. 

d . Must be protected by dead insulated guard iron or wires from possibility 

of contact with other conducting wires or substances to which current 
may leak. 

e. Must be provided with petticoat insulators only, glass or porcelain. 

f. Must be so joined as to be both mechanically and electrically secure with¬ 

out solder ; joints must then be soldered, and covered with an insula¬ 
tion equal to that of the conductors. 

g. Must, where they enter buildings, have drip-loops, and the holes bushed with 

non-combustible, non-absorptive tubes slanting upward toward the inside. 

h. Telegraph, telephone, or similar wires must not be placed on the same cross- 

arm with electric light or power circuits. 

i. The metal sheaths of cables must be permanently grounded. 

Trolley Wires. 

Must not be smaller than No. 0 B. & S. copper or No. 4 B. & S. silicon 
bronze, and must readily stand the strain put upon them when in use. 
Must have a double insulation from ground. In wooden-pole construction, 
the pole will be considered as one insulation. 

Must be capable of being disconnected at the power-plant or of being sub¬ 
divided into sections. This rule also applies to feeders. 
m. Must be protected against accidental contact where crossed by other con¬ 
ductors. 13 Trans fo rm ers. 

a. Must not be placed inside of any building excepting central stations. 

b. Must not be attached to the outside wall of buildings unless separated by 

substantial supports. 

125. Class C. Inside Work. a. General Instructions. 14. Wires. 

a. Must not be smaller than No. 14 B. & S., except as specified under 24-u 

and 40-c. 

b. Tie-wires must have an insulation equal to that of the conductors. 

c. Must be joined so as to be mechanically and electrically secure without 

solder, and then soldered, and covered with an insulation equal to that of 


J 


k. 


1 . 


128 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


the conductors. Stranded wires must be soldered before being fastened 
under clamps or binding-screws ; and, when they have a greater conduc¬ 
tivity than No. 10 B. & S. copper wire, they must be soldered into lugs. 
(I. Must be separated from contact with all portions of the building through 
which they pass by non-combustible, non-absorptive, insulating-tubes. 
e. Must be kept free from contact with all other conducting material by a 
continuous, firmly fixed non-conductor, providing a separation of at 
least one inch. 

f Must be so placed in damp places that moisture cannot form crosses 
between conductors or between the conductors and other things. 

15. Underground Conductors. 

a. Must be protected, when entering buildings, against moisture and me¬ 

chanical injury, and all combustible material kept removed from the 
immediate vicinity. 

b. Must not be so arranged as to shunt the current around any protective 

device. 


126. 16. Table of Carrying Capacity of Wires. 


. & S. G. 

18 . 



Table A. 

Rubbek- 

COVEKED 

Wires. 

See No. 40 , a . 
Amperes. 

3 . 

16 . 



6 . 

14 . 



. 12 . 

12 . 



. 17 . 

10 . 



. 24 . 

8 . 



. 33 . 

6 . 



. 46 . 

5 . 



. 54 . 

4 . 



. 65 . 

3 . 



. 76 . 

2 . 



. 90 . 

1 . 



. 107 . 

0 . 



. 127 . 

00 . 



. 150 . 

000 . 



. 177 . 

0000 . 



. 210 . 


Table B. 

Weather¬ 

proof 

Wires. 

See No . 40 , b . 


Amperes. 

Circular Mills 

5 

200,000 . 

8 

300,000. 

. 16 

400,000. 

. 23 

500,000. 

. 32 

600,000. 
700,000 . 

. 46 

. 65 

800,000 . 

. 77 

900,000 . 

. 92 

1,000,000. 

. 110 

1,100,000 . 

. 131 

1,200,000. 

. 156 

1,300,000. 

. 185 

1,400,000 . 

. 220 

1,500,000 . 

. 262 

1,600,000 . 

. 312 

1,700,000 . 
1,800,000 . 
1,900,000 . 
2,000,000. 


Table A. 

Table B. 

Rubber- 

Weather¬ 

Covered 

proof 

Wires. 

Wires. 

See No . 40 , a . 

See No . 40 , b . 

Amperes. 

Amperes. 

. 200. 

. 300 

. 270. 

. 400 

. 330. 

. 500 

. 390. 

. 590 

. 450 . 

. 680 

. 500. 

. 760 

550. 

. 840 

. 600. 

. 920 

. 650. 

. 1,000 

. 690. 

. 1,080 

. 730. 

. 1,150 

. 770. 

. 1,220 

. 810. 

. 1,290 

. 850. 

. 1,360 

. 890. 

. 1,430 

. 930. 

. 1,490 

. 970. 

. 1,550 

. 1,010 . 

. 1,610 

. 1,050. 

. 1,670 


127. 17. Switches, Cut-outs, and Circuit-Breakers. 

a. Must be so arranged that each cut-out switch or circuit-breaker will dis¬ 

connect all the wires of the circuit to which it is attached. 

b. Must not be placed in the immediate vicinity of inflammable material. 

c. Must, when exposed to dampness, be inclosed in waterproof box or 

mounted on non-absorptive material. 


128. ( b ) Constant-Current Systems. 18. Wires. 

a. Must have an approved rubber insulation. 

b. Must be arranged to enter and leave buildings through an approved dou¬ 

ble-contact service switch kept free from moisture and of easy access. 
Snap-switches must not be used. 

c. Must always be arranged in plain sight and not incased. 












INSURANCE REGULATIONS FOR CIRCUITS . 


129 


d Must be supported upon glass or porcelain insulators, which separate the 
wire at least one inch from surface, wired over, and be kept rigidly eight 
inches from each other, except within the structure of lamps or on 
hanger-boards. 

e. Must, on side walls, be protected from mechanical injury by boxing in¬ 
closing an air-space of at least one inch all around the conductors. 
The boxing must be closed at the top, the wires passing through bushed 
holes, and must extend not less than seven feet from the floor. When 
crossing floor-timbers where the conductors might be exposed to injury, 
wires must be attached by their insulating supports to the under side of 
a wooden strip not less than one-half an inch in thickness. 

19. Arc Lamps. 

a. Must be carefully isolated from inflammable material. 

b. Must always be provided with whole-glass globes inclosing the arc, se¬ 

curely fastened on a closed base. 

c. Must be provided with a wire netting of not over inch mesh and an 

approved spark-arrester, when inflammable material is in the vicinity 
of the lamps. 

d. Where hanger-boards are not used, lamps must be hung from insulating 

supports other than their conductors. 

20. Incandescent Lamps in Series Circuits. 

a. Must have the conductors installed as provided for in Rule 18. Each 

lamp is to be provided with an automatic cut-out, and 

b. Suspended from a hanger-board by means of a rigid tube. 

c. Electro-magnetic devices for switches and systems of multiple-series or 

series-multiple lighting must not be used. 

d. Must not be attached to gas-fixtures. 

129. (c) Constant-Potential Systems, All Voltages. 

21. Automatic Cut-outs. 

a. Must be placed on all service-wires as near as possible to the point where 

they enter the building, inside the walls, and arranged to cut off the 
entire current. 

b. Must be placed at every point where change is made in the size of the 

wire, unless the cut-out in larger wire will protect the smaller. 

c. Must be in plain sight, or inclosed in an approved box readily accessible. 

Must not be placed in the canopies or shells of fixtures. 

d. Must be so placed that no set of incandescent lamps requiring more than 

6 amperes shall be dependent upon one cut-out. 

e. Must be provided with fuses, the capacity of which does not exceed the 

allowable carrying capacity of the wire. Circuit-breakers must not be 
set more than 30 per cent above the allowable carrying capacity of the 
conductors they protect. 

22. Switches. 

a. Must be placed on all service-wires, in a readily accessible place, as near as 

possible to the point where the wires enter the building, and arranged to 
cut off the entire current. 

b. Must always be placed in dry, accessible places, and grouped as far apart 

as possible. Knife-switches must be so placed that gravity will tend to 
open the switch. 


130 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


c. Must be double-pole except when the circuits they control supply 3 am¬ 

peres or less. 

d. Gangs of flush-switches must be inclosed in boxes of fire-resisting mate¬ 

rial. Where two or more switches are placed under one plate, the box 
must have a separate compartment for each. No push-buttons for bells, 
gas-lighting circuits, etc., shall be placed in the same wall-plate with 
switches controlling lighting or power circuits. 

23. Electric Heaters. 

a. Must be placed at a safe distance from inflammable material, and be 

treated as sources of heat. 

b. Each must have a cut-out and indicating-switch. 

c. Must have the attachment of feed-wires in plain sight, easily accessible, 

and protected from interference. 

d. Flexible conductors for portable apparatus must have an approved insu¬ 

lating covering. 

e. Each must be provided with a name-plate giving maker and normal capa¬ 

city in volts and amperes. 

130. 2. Low-Potential Circuits. 

Voltages not over 300. (Any circuit which develops a difference of poten¬ 
tial between 10 and 300 volts shall be considered a low-potential circuit.) 

24. Wires. 

a. Must not be laid in cement, plaster, or similar finish. 

b. Nor fastened with staples. 

c. Nor be fished for any great distance, and only where inspectors can be 

satisfied that rules are complied with. 

d. Twin wires must not be used excepting in conduits or where flexible con¬ 

ductors are necessary. 

e. Must be protected on side walls from mechanical injury, and protected 

when crossing floor-timbers by attaching the wires by their insulating 
supports to the under side of a wooden strip, not less than one-half inch 
thick and not less than three inches wide. 

f When run immediately under roofs, or near water pipes or tanks, they will 
be considered as exposed to moisture. 

Special Rules for Dry Places. 

g. Must have an approved rubber or weatherproof insulation. 

h. Must be rigidly supported on non-combustible, non-absorptive insulators, 

which separate the wires at least one-half inch from the surface wired 
over, and two and one-half inches from each other. 

Special Rules for Damp Places. 

i. Must have an approved rubber insulation. 

j. Must be rigidly supported on insulators which separate the wires at least 

one inch from the surface wired over, and two and one-half inches from 
each other. 

k. Must have no joints or splices. 

For Molding Work. 

/. Must have an approved insulation. 
m. Must never be placed in molding in concealed or damp places. 


INSURANCE REGULATIONS EOR CIRCUITS. 


181 


For Conduit Work. 

n. Must have approved insulation. 

o. Must not be drawn in until all mechanical work on the building is completed. 
ft. Must not have wires of different circuits drawn in the same conduit. 

q. Must, for alternating systems, have all wires of the same circuit drawn in 

the same conduit. This is advised for direct-current systems. 

For Concealed Work. 

r. Must have an approved rubber insulation. 

s. Must be rigidly supported upon non-combustible, non-absorptive insulators, 

which separate the wires at least one inch from the surface wired over, 
and ten inches from each other. 

/. When it is impossible to place concealed wiring on non-combustible sup¬ 
ports, the wires, if not exposed to moisture, may be fished on the loop- 
system, if inclosed in approved continuous flexible tubing or conduit. 

For Fixture Work. 

u. Must have approved rubber insulation, and shall not be less than No. 18 

B. & S. in size. 

v. Supply conductors must be kept clear of the grounded parts of fixtures. 

Shells must be constructed in a manner to permit of this requirement. 

w. Must, when fixtures are wired outside, be so secured as not to be cut or 

abraded by the motion of the fixtures. 

25. Interior Conduits. 

a . Must be continuous from one junction to another or to fixtures, and the 

conduit tube must properly enter all fittings. 

b. Must be first installed as a complete conduit system without conductors. 

c. Conduits must extend at least one-half inch beyond the finished surface 

of walls or ceilings, except that, if the end is threaded and a coupling 
screwed on, the conduit may be left flush. 

d. Must, after conductors are introduced, have all outlets plugged with special 

wood or fibrous plugs, made in parts, and the outlet then sealed with 
approved compound. Joints must be air-tight and moisture-proof. 

e . Must have the metal of the conduit permanently and effectually grounded. 

26. Fixtures. 

a . Must, when supported from the gas-piping, be insulated from the gas-pipe 

system by means of approved insulating joints. 

b. Must have all burs or fins removed before the conductors are drawn into 

the fixture. 

c. The upper end of all fixtures must be sealed moisture-proof. 

d. Combination fixtures must not conceal the conductors in a space less than 

one-fourth inch. 

e. Must test free from contacts between conductors and fixtures, from short 

circuits, and from grounds. 

f Ceiling-blocks should be made of insulating material; or if not, the wires 
passing through the plates must be surrounded with non-combustible, 
non-absorptive, insulation. 

27. Sockets. 

a . Where inflammable gases exist, the lamp and socket must be inclosed in a 
vapor-tight globe, wired with approved rubber-covered wire soldered 
directly to the circuit. 


132 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


b. In damp places or over specially inflammable stuff, waterproof sockets 
must be used. 28. Flexible cord. 

a. Must have approved insulation and covering. 

b. Must not be used as a support for clusters. 

c. Must not be used except for pendants, wiring of fixtures, or portable lamps 

or motors. 

d. Nor in show-windows. 

e. Must be protected by insulating bushings where the cord enters the socket. 

f. Must be so suspended that the entire weight of the sockets will be borne 

by knots under the bushing in the socket, and above the point where the 
cord comes through the ceiling-block or rosette. 

29. Arc Lights cn Low-Potential Circuits. 

a. Must have a cut-out for each lamp or series of lamps. 

b. Must be furnished with such resistances or regulators as are inclosed in 

non-combustible material. Incandescent lamps must not be used for 
resistances. 

c. Must be supplied with globes, and protected by spark-arresters. 

30. Economy Coils. 

a. Economy and compensator coils must be mounted on non-combustible, 
non-absorptive insulating supports, allowing an air-space of at least one 
inch between the frame and support, and in general treated as sources 

of heat. 31. Decorative Series Lamps. 

a. Incandescent lamps in series shall not be used excepting by special per¬ 
mission. 

131. 3. High-Potential Circuits. ✓ I'oltages between 300 and 3,000. 

32. Wires. 

a. Must have approved rubber insulation. 

b. Must alwavs be in plain sight, and never incased except where required by 

the inspection department. 

c. Must be rigidly supported on glass or porcelain insulators carrying the 

wires at least one inch from the surface wired over, and at least four 
inches apart for voltages up to 750 and at least eight inches apart for 
voltages over 750. 

d. Must be protected on side walls from mechanical injury by substantial 

boxing, retaining an air-space of one inch around the conductors, closed 
at the top, the wires passing through bushed holes, and extending not 
less than seven feet from the floor. When crossing floor-timbers wires 
must be attached by their insulating supports to the under side of a 
wooden strip not less than one-half inch in thickness. 

33. Transformers Must Be Placed — 

a. At a point as near as possible to that at which the primary wires enter 

the building. 

b. In an inclosure constructed or lined with fire-resisting material, this in¬ 

closure to be securely locked, and access allowed only to responsible 
persons. 

c. Effectually insulated from the ground and in a practically air-tight inclo¬ 

sure, except that it shall be thoroughly ventilated to the outdoor air, and 
there must be a six-inch air-space on all sides of the transformer. 


INSURANCE REGULATIONS EOR CIRCUITS. 


133 


34. Car-Wiring. 

a. Must always be run out of reach of passengers, and have an approved 
rubber insulation. 

132 . 35. Car-Houses. 

a. Must have the trolley-wires securely supported on insulating hangers. 

b. Must have the trolley-hangers placed at such a distance apart that in case 

of a break in the trolley-wire, contact could not be made with the floor. 

c. Must have cut-out switch located at proper place outside the building, so 

that all trolley circuits in the building can be cut out at one point, and line 
circuit-breakers must be installed, so that when this cut-out switch is open 
the trolley-wire will be dead at all points within 100 feet of the building. 
The current must be cut out of the building whenever not in use. 

d. Must have all lamps and stationary motors installed so that one main 

switch can control the whole of each installation, independently of main 
feeder-switch. No portable incandescent lamps or twin wires allowed 
except that portable incandescent lamps may be used in the pits, con¬ 
nections to be made by two approved flexible rubber-covered wires 
properly connected, and controlled by a switch placed outside the pit. 

e. Must have all wiring and apparatus installed in accordance with rules 

under Class C. 

f. Must not have any system of feeder distribution centering in the building. 

g. Must have the rails bonded at each joint with not less than No. 2 B. & S. 

annealed copper wire; also a supplementary wire to be run for each 
track. 

h. Must not have cars left with trolley in electrical connection with the trol¬ 

ley-wire. 

133 . 36. Lighting and Power from Railway Wires. 

a. Must not be permitted under any pretense in the same circuit with trolley- 
wires with a ground return except in electric railway cars, electric car- 
houses and their power-stations, nor shall the same dynamos be used 
for both purposes. 

37. Series Lamps. 

a. No system of multiple-series or series-multiple for light or power shall be 

used. 

b. Under no circumstances can lamps be attached to gas-fixtures. 

134. 4. Voltages over 3,000. 38. Primary Wires. 

Must not be brought into or over buildings except power- and sub-stations. 

39. Secondary Wires. 

a. Must be installed under Rules for high-potential systems when their im¬ 
mediate primary wires carry a current at a potential of over 3,000 volts. 

135. Class D. Fittings, Materials, and Details of Construction. 

All Systems and Voltages. 

40. Wire Insulation. 

a. Rubber-Covered. — The insulating covering must be solid, at least g 3 T of an 
inch thick, and covered with a substantial braid. Must not readily 
carry fire, must show an insulation of one megohm per mile after two 
weeks’ submersion in water at seventy degrees Fahrenheit, and three 
days’ submersion in lime-water, and after three minutes’ electrification 
with 550 volts. 


184 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


b. Weatherproof. — The insulating covering must not support combustion, 

must resist abrasion, must be at least one-sixteenth of an inch thick, and 
thoroughly impregnated with a moisture-repellent. 

c. Flexible Cord. — Must be of two-stranded conductors, each having a car¬ 

rying capacity of not less than a No. 10 B. & S. wire, and each covered 
by an approved insulation, and protected by a slow-burning, tough- 
braided outer covering. 

1. Insulation for pendants must be moisture and flame proof. 

2. Insulation for all other purposes must be solid, at least of an inch 

thick, and must show an insulation resistance between conductors 
and between either conductor and the ground of at least one megohm 
per mile after one week's submersion in water at 70° Fahrenheit, 
and after three minutes’ electrification with 550 volts. 

3. The flexible conductors for portable heating-apparatus must have an 

insulation that will not be injured by heat, which must be protected 
from mechanical injury by an outer substantial braided covering, 
and so arranged that mechanical strain will not be borne by the 
electrical connection. 

d. Fixture Wire. — Must have a solid insulation, with a slow-burning, tough 
outer covering, the whole to be at least of an inch thick, and show an 
insulation between conductors and between either conductor and ground 
of at least one megohm per mile, after one week’s submersion in water 
at 70° Fahrenheit, and after three minutes’ electrification with 550 volts. 

e. Conduit Wire. — 1. For insulated metal conduits, single wires and twin con¬ 
ductors must comply with Section a of these Rules. Concentric wire 
must have a braided covering between the outer conductor and the 
insulation of the inner conductor, and must comply with Section a. 

2. For non-insulated metal conduits, single wires and twin conductors must 
comply with section a , and in addition have a second outer fibrous 
covering at least ^ of an inch thick, and sufficiently tenacious to 
withstand the abrasion of being hauled through the metal conduit. 
Concentric conductors must have a braided covering between the 
outer conductor and the insulation of the inner conductor, and 
comply with section a of this rule, and must have a fibrous cover¬ 
ing of an inch thick, and sufficiently tenacious to withstand the 
abrasion of being hauled into the conduit. 

136- 41. Interior Conduits. 

a. Each length of conduit must have the maker’s name or initials stamped in 

the metal so that inspectors can see the same. 

Insulated Metal Conduits. 

b. The metal covering must have an equal resistance to penetration by nails 

as the ordinary commercial form of gas-pipe of same size. 

c. Must not be seriously affected by burning out a wire inside the tube when 

the metal is connected to one side of the circuit. 

d. Must have the insulating lining firmly secured. 

e. The insulating lining must not crack or break when a length of conduit is 

uniformly bent, at temperature of 212° Fahrenheit, to an angle of 90° 
with a curve of fifteen inches radius, for pipes of one inch and less, and 
fifteen times the diameter of pipe for larger pipes. 

f The insulating lining must not soften injuriously at a temperature below 
212° hahrenheit, and must leave the water in which it is boiled practi¬ 
cally neutral. 


INSURANCE REGULATIONS FOR CIRCUITS . 


18 f> 

g. The insulating lining must be at least 3 V of an inch thick, and the materials 

composing it must be of such a nature as will not have a deteriorating 
effect on the insulation of the conductors, and must be sufficiently tough 
to withstand the abrasion of drawing in and out of long lengths of con¬ 
ductors. 

h. The insulating lining must not be mechanically weak after three days’ sub¬ 

mersion in water, and when removed from the pipe entire must not 
absorb more than ten per cent of its weight of water during 100 hours 
of submersion. 

i. All elbows must be made for the purpose, and not bent from lengths of 

pipe. The inner radius of any elbow of pipe must not be less than 3| 
inches. Must not have more than the equivalent of four quarter bends 
from outlet to outlet, the bends at the outlets not being counted. 

Uninsulated Metal Conduits. 

j. Plain iron or steel pipes of equal strength to resist penetration by nails as 

ordinary gas-pipe of the same size, provided the interior surfaces are 
smooth and free from burs, may be used. Pipe to be galvanized, or the 
interior surfaces coated, to prevent oxidization, with some substance 
which will not become sticky, and prevent wire from being withdrawn. 

k. Ml elbows must be made, and not bent from lengths of pipe. The inner 

radius of any elbow must not be less than 34 inches. Must have not 
more than the equivalent of four quarter bends from outlet to outlet, the 
bends at the outlets not being counted. 

137 - 42. Wooden Moldings. 

a. Must have, both inside and outside, at least two coats of waterproof paint, 

or be impregnated with a moisture-repellent. 

b. Must be made of two pieces, backing and capping constructed to thoroughly 

incase the wire, and provide a one-half inch tongue between conductors 
and a solid backing, which under-grooves shall not be less than three- 
eighths of an inch thick, and must afford suitable protection from abra- 

S10n * 138 . 43. Switches. 

a . Must be mounted on non-combustible, non-absorptive bases. 

b. Must have carrying capacity sufficient to prevent undue heating. 

c. Must, when used for service-switches, indicate whether the current is on 

or off. 

d. Must be plainly marked with the name of the maker and the current and 

voltage for which the switch is designed. 

e. Must, for constant-potential systems, operate successfully at 50 per cent 

overload, in amperes, with 25 per cent excess voltage under the most 
severe conditions to be met with in practice. 
f Must, for constant-potential systems, have a firm and secure contact; must 
make and break readily, and must not stop when motion has once been 
imparted by the handle. 

g. Must, for constant-current systems, close the main circuit and disconnect 
the branch wires when turned “ off ” ; must be constructed to be auto¬ 
matic in action, not stopping between points when started, and must 
prevent an arc under all circumstances. Must indicate whether the 
current is on or off. 

139 . 44. Cut-outs and Circuit-Breakers. 

a. Must be supported on bases of non-combustible, non-absorptive insulating 
material. 


136 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


b. 


c. 


d 


e. 


a. 


b. 


c. 


a. 


a. 


b. 


a. 


a. 


b. 


c. 


a. 


a. 


b. 


Cut-outs must be provided with covers when not arranged in approved 
cabinets. 

Cut-outs must operate successfully with fuses rated at 50 per cent above 
and voltage 25 per cent above that for which they are designed, under 
the most severe conditions of practice. 

Circuit-breakers must operate successfully with a current 50 per cent above 
and a voltage 25 per cent above that for which they are designed, under 
the most severe conditions of practice. 

Must be plainly marked with the name of the maker and current and 
voltage for which designed. 

45. Fuses. 


Must have contact surfaces or tips of harder metal having perfect elec¬ 
trical connection with the fusible part. 

Must be stamped with about 80 per cent of the maximum current they can 
carry indefinitely. 

Fuse terminals must be stamped with the maker’s name, initials, or known 


trade-mark. 


46. Cut-out Cabinets. 


Must be so arranged as to obviate any danger from melted fuses. 


140 . 47. Sockets. 

No portion of the lamp-socket exposed to contact with outside objects 
must be allowed to come into electrical contact with either conductor. 
Must, when provided with keys, comply with the requirements for switches. 


141 . 48 . Hanger-Boards. 

Hanger-boards must be so constructed that all wires and current-carrying 
devices thereon shall be exposed to view, and thoroughly insulated by 
being mounted on a non-combustible, non-absorptive insulating sub¬ 
stance. 

All switches shall be double-pole automatic in action and strictly non- 
arcing. 142 - 49. Arc Lamps. 

Must be provided with reliable stops to prevent carbons from falling out, 
in case clamps become loose. 

Must be carefully insulated from the circuit in all exposed parts. 

Must, for constant-current systems, be provided with an approved hand- 
switch, also an automatic switch that will shunt the current if they 
fail to feed properly. The hand-switch, if placed anywhere except on 
the lamp itself, must comply with Rule 48. 


143 . 50. Spark-Arresters. 

Spark-arresters must so close the globe that it will be impossible for any 
sparks to escape. 

144 . 51. Insulating-Joints. 

Must be entirely made of material that will resist the action of illuminating 
gases, and will not soften under the heat of an ordinary gas-flame, or leak 
under moderate pressure, and arranged so that a deposit of moisture 
will not destroy the insulation, and shall have a resistance of not less 
than 250,000 ohms, and be sufficiently strong to resist the strain to which 
they will be subjected. 

Insulating-joints employing soft rubber will not be allowed. 


x 


INSURANCE REGULATIONS EOR CIRCUITS. 


137 


145 . 52. Resistance Boxes and Equalizers. 

a. Must be equipped with metal or with other non-combustible frames. 

146 . 53. Reactive Ceils and Condensers. 

a. Reactive coils must be made of non-combustible material, and treated as 
sources of heat. 

147. 54. Transformers. 

a . Must not be’ placed in any but metallic or non-combustible cases. 


148. 55. Lighting-Arresters. 

a. Must be mounted on non-combustible bases, and must be so constructed 
as not to maintain an arc after the discharge has passed, and must have 
no moving parts. 

149. Class E. Miscellaneous. 56. Insulation Resistances. 


All wiring in buildings must test free from grounds, and must have an insula¬ 
tion between conductors and between all conductors and ground as follows. Cir¬ 


cuits carrying current up to — 

5 amperes . . 4,000,000 ohms. 

10 amperes . . 2,000,000 ohms. 

25 amperes . . 800,000 ohms. 

50 amperes . . 400,000 ohms. 

100 amperes . . 200,000 ohms. 


200 amperes . . 100,000 ohms. 

400 amperes . . 50,000 ohms. 

800 amperes . . 25,000 ohms. 

1,000 amperes, and over, 

12,500 ohms. 


All cut-outs and safety devices must be in place when test is made. When 
lamp-sockets, receptacles, and electroliers, etc., are connected, one-half of the 
above insulation will be required. 


150. 57. Protection Against Foreign Currents. 

a. Where telephone, telegraph, or other wires connected with outside circuits 

are bunched together within a building, and where inside wires are laid 
in ducts with lighting or power wires, covering of such wires must be 
fire-resisting or they must be inclosed in air-tight ducts. 

b. All conductors under (a) which run to aerial lines must be provided with 

approved protective devices which will shunt the instruments in case of 
a dangerous rise of potential, and will open the circuit and arrest abnor¬ 
mal current. Protectors must have non-combustible insulating bases, 
and covers provided with a lock, and must be installed under the follow¬ 
ing requirements : — 

1. Protectors must be located at the point where the wires enter the build¬ 

ing, either immediately inside or outside the same. If outside, the 
protector must be inclosed in a metallic waterproof case. 

2. If protectors are placed inside the building, the wires from the support 

outside to the binding-post of the protector shall be of a grade of 
insulation equal to that of electric light or power wires, and the holes 
through the outer wall must be bushed as for high-tension service. 

3. The wires from the point of entrance to the protector must be run in 

accordance with rules for high-potential wires. 

4. Ground wires shall be insulated, not smaller than No. 16 B. & S. 

Ground wires shall be kept at least three inches from all conductors, 
and run in as straight a line as possible to the ground. 

5. Ground wires shall be attached to a water-pipe if possible, and shall be 

carried to and attached to the pipe outside the first joint inside of 
the foundation walls, and connection be made by soldering. In the 




138 


THE ELECTRICAL TRANSMISSION OF ENERGY . 


absence of other good ground, the ground shall be made by means 
of a metallic plate buried permanently in moist earth. 


58. Electric Gas-Lighting. 

Where electric gas-lighting is to be used on the same fixture with the electric 
light — 

a . No part of the gas-piping or fixture shall be in electric connection with the 

gas-lighting circuit. 

b. The wires shall have non-inflammable or, when concealed, such insulation 

as required for fixture-wiring for electric lights. 

c. The whole insulation must test free from grounds. 

d. The two insulations must test perfectly free from connection with each 

other. 


a. 

b. 


c. 

d. 


151. Class F. Marine Work. 60. Generators must be — 

Located in a dry place. 

Insulated from their bed-plates. 

Provided with waterproof cover, and — 

With name-plate, giving the maker, voltage, amperes, and normal speed 


R. P. M. 


152. 61. Wires. 


a. Must have an approved insulation, not less than | inch thick for all con¬ 

ductors except portables, and covered with substantial water-and flame¬ 
proof braid. The physical characteristics shall not be affected by any 
change in temperature up to 200° Fahrenheit. After two weeks’ sub¬ 
mersion in salt water at 70° Fahrenheit, it must show an insulation resis¬ 
tance of one megohm per mile after three minutes’ electrification with 
550 volts. 

b. Must have no single wire larger than No. 12 B. & S. Stranded conduc¬ 

tors must be used when greater carrying capacity is required. No sin¬ 
gle solid wires smaller than No. 14 B. & S., excepting in fixture-wiring. 
Stranded wires must be soldered before being fastened under binding- 
screws. When they have a greater conductivity than No. 10 B. & S., 
they must be soldered into lugs. 

c. Must be supported in approved molding except at switches and portables. 

d. Must be bushed with hard-rubber tubing one-eighth of an inch thick when 

passing through beams and non-watertight bulkheads. 

e. Must have, when passing through watertight bulk-heads and through all 

decks, a metallic-box tube lined with hard rubber. In case of deck- 
tubes they shall be boxed to prevent mechanical injury. 
f Necessary splices or taps must be made both electrically and mechanically 
secure without solder. They must then be soldered, and covered with 
an insulating compound equal to that of the wire, and protected by 
waterproof tape, and then painted with waterproof paint. 

153. 62. Portable Conductors. 

a. Must be made of two-stranded conductors, each having a carrying-capa¬ 
city equivalent to No. 14 B. & S. wire, and covered with an approved 
insulation. When not exposed to moisture or severe mechanical injury, 
each conductor must have a solid insulation, at least of an inch thick, 
and must show an insulation between conductors and between each 
conductor and ground of at least one megohm per mile after one week’s 
submersion in water at seventy degrees and after three minutes’ electri¬ 
fication at 550 volts, and be protected by slow-burning, tough-braided 


INSURANCE REGULATIONS EOR CIRCUITS . 


139 


covering. Where exposed to moisture or mechanical injury, each con¬ 
ductor shall have at least of an inch solid insulation protected by 
tough braid. The two conductors shall then be stranded together, 
using a jute filling. The whole shall be covered with a layer of flax, 
at least g 1 ^ of an inch thick, and treated with a non-inflammable, water¬ 
proof compound. After one week’s submersion in water at seventy 
degrees, with 550 volts and a three minutes’ electrification, must show 
an insulation between the two conductors, or between each conductor 
and the ground, of one megohm per mile. 

63. Bell or Other Wires. 

a. Shall never be run in the same duct with lighting or power circuits. 


154. 64. Table of Capacity of Wires. 


B. & S. G. 

Area. 

Actual 

C. M. 

No. OF 

Strands. 

Size of 
Strands. 

B. & S. G. 

Amperes. 

B. & S. G. 

Area. 

Actual 

C. M. 

No. OF 

Strands. 

Size of 

Strands. 

B. & S. G. 

Amperes. 

19 

1,288 



, , 


38,912 

19 

17 

60 

18 

1,624 



3 


49,077 

19 

16 

70 

17 

2,048 



• 0 


60,088 

37 

18 

85 

16 

2,583 



6 


75,776 

37 

17 

100 

15 

3,257 



• • 


99,064 

61 

18 

120 

14 

4,107 



12 


124,928 

61 

17 

145 

12 

6,530 



17 


157,563 

61 

16 

170 


9,016 

7 

19 

21 


198,677 

61 

15 

200 


11,368 

7 

18 

25 


250,527 

61 

14 

235 


14,336 

7 

17 

30 


296,387 

91 

15 

270 


18,081 

7 

16 

35 


373,737 

91 

14 

320 


23,709 

7 

15 

40 


413,639 

127 

15 

340 


30,856 

19 

18 

50 







When greater conducting area than that of 12 B. & S. G. is required, the con¬ 
ductor shall be stranded in a series of 7, 19, 37, Gl, 91, or 127 wires, as may be 
required; the strand consisting of one central wire, the remaining laid around it 
concentrically, each layer to be twisted in the opposite direction from the preceding. 

155. 65. Switchboards. 

a. Must be of non-combustible, non-absorptive insulating material. 

b. Must be kept free from moisture, and accessible from all sides. 

c. Must have a main switch, cut-out, and ammeter for each generator, a volt¬ 

meter, and ground conductor. 

d. Must have a cut-out and switch for each side of each circuit. 

156. 66. Resistance Boxes. 

a. Must be non-combustible material. 

b. Must be mounted on non-inflammable, non-combustible material, preferably 

on the switchboard. 

c. Must be constructed to allow sufficient ventilation. 

157. 67. Switches. 

a. Must have non-combustible, non-absorptive bases. 

b. Must operate successfully at 50 per cent overload in amperes, with 25 per 

cent excess voltage under the most severe conditions, and must be plainly 
marked with the name of the maker, current, and voltage. 






























140 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


c. 


d. 


a. 

b. 


c. 


d. 


e. 


f 


a. 


b. 


c. 


a. 


a. 


b. 


c. 


d. 


a. 


b. 


c. 

d. 


Must be double-pole when circuits which they control supply more than six 
10 -candle-power lamps or their equivalent. 

Must, when exposed to dampness, be inclosed in a watertight case. 


158. 68. Cut-outs. 

Must have non-combustible, non-absorptive insulating bases. 

Must operate successfully on short circuits, with fuses rated at 50 per cent 
above and with a voltage 25 per cent above the current and voltage for 
which they were designed, and must be plainly marked with the name 
of maker, current, and voltage. 

Must be placed at every point where a change is made in the size of the 
wire, unless the cut-out in the larger wire will protect the smaller. 

In places such as upper decks, holds, cargo spaces, and fire-rooms, a water¬ 
tight and fireproof cut-out may be used, connecting directly to mains 
when such cut-out supplies not more than six 16-candle-power lamps or 
their equivalent. 

When placed anywhere except on switchboards and places as specified in 
d, they shall be in a cabinet lined with fire-resisting material. 

Shall be so placed, except for motors, search-lights, and diving-lamps, that 
no group of lamps requiring more than six amperes shall depend upon 


one cut-out. 


159. 69. Fixtures. 


Shall be mounted on blocks of well-seasoned lumber, treated with two coats 
of w'hite lead or shellac. 

Where exposed to dampness, the lamp must be surrounded by a vapor- 
proof globe, and where exposed to mechanical injury, surrounded by a 
globe protected by a stout wire guard. 

Shall be wired with the same grade of insulation as portable conductors 
which are not exposed to moisture or mechanical injury. 


160. 70. Sockets. 

No portion of the lamp-socket which is exposed to contact with outside 
objects shall come into electrical contact with either of the conductors. 


161. 71. Wooden Moldings. 

Must be of well-seasoned lumber, and treated inside and out with two coats 
of white lead or shellac. 

Must be made in two pieces, so constructed as to thoroughly incase the 
wire, and provide a one-half inch tongue between conductors and a solid 
backing under grooves not less than three-eighths of an inch thick. 

Where molding is run over rivets, beams, etc., it must be secured to a 
backing-strip. 

Capping must be secured by brass screws. 


162. 72. Motors. 

Must be wired under the same rules as apply to circuits of the same cur¬ 
rent and potential for lighting. The motor and resistance-box must be 
protected by a double-pole cut-out, and controlled by a double-pole 
switch, unless of one-quarter horse-power or less. 

Must be thoroughly insulated. 

Shall be covered with waterproof covers when not in use. 

Must be provided with a name-plate, with maker’s name, capacity in volts 
and amperes, and the normal speed in revolutions per minute. 


THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


141 


CHAPTER IV. 

THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 

PART I.—CONDUITS. 

163. The rapid multiplication of electrical circuits, particularly 
in business centers of the large towns, has increased the number of 
aerial wires to such an extent as to become an unbearable street ob¬ 
struction. To obviate this difficulty the practice has arisen of con¬ 
structing underground subways, or conduits, into which circuits may 
be placed. 

164. Classification. — Conduits can be divided into two classes, 
that may, respectively, be termed flexible and inflexible systems, 
depending upon the possible mutability of the circuits after the 
structure is completed. 

In the flexible system, a structure is designed and built under 
the pavement of the street in such a manner that the electrical 
circuits which it is to contain may be introduced at any time after 
the completion of the subway ; and from time to time the circuits 
may be extended, or rearranged or replaced, as the business of the 
territory shall indicate to be advisable. 

Under the inflexible system, as the conduit is built, all of the 
wires which it can ever contain are introduced at the time of con¬ 
struction, the design being such as to preclude any modification 
of the circuits after the completion of the work. In thickly set¬ 
tled districts, where the amount of electrical business can be fairly 
accurately gauged, and in which the changes or extensions in the 
business, beyond that of the original estimate, are small from year to 
year, the inflexible system presents the advantage of cheapness in 
initial construction. The design of the structure must contemplate, 
however, sufficient capacity to embrace all of the probable business 
which is ever likely to be done, for increased capacity can only be 
secured by constructing an entirely new conduit. The inflexible 
system being more economically constructed, and of more economical 


142 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


maintenance, presents the attractiveness of cheapness, though, unless 
the amount of business can be accurately gauged and located, this 
very quality is apt to prove deceptive, and the subsequent cost of 
extension and rearrangement may greatly exceed the initial expense 
of a flexible system. 

With the flexible system, the subways are designed with suffi¬ 
cient room to be capable of receiving all of the circuits which the 
most sanguine estimate of the business of the future can call for. 
The conduits are planned with a number of separate chambers, or 
ducts, into which the circuits may be placed. The expense, there¬ 
fore, of the conductors can be reserved until business shall demand 
their introduction. 

Every form of conduit should embrace the following condi¬ 
tions : — 

The conduit should be reasonably economical in cost of con¬ 
struction. 

It should afford a thorough protection to the inclosed circuits, 
securing them from the effects of street excavations, and from the 
incursion of gas, water, or organic acids from the streets, and should 
protect the insulation of the circuits, and maintain it at a high 
working average. 

It must be rapid and easy of construction, so as not to present 
undue obstruction to street traffic. 

It must be sufficiently flexible to accommodate itself to existing 
street structures. 

It must have sufficient mechanical strength to successfully resist 
the ordinary destructive influences to which street structures are 
exposed. 

It must present a minimum annual maintenance expense. 

165. The Valentine Conduit. — One of the earliest underground 
distributions was the Valentine system, consisting of a rectangular 
wooden box some ten to fifteen feet in length, subdivided by ver¬ 
tical and horizontal partitions, into ducts about three inches square, 
for the reception of the circuits. These boxes were constructed of 
creosoted yellow pine, and were buried in the earth at a safe distance 
below the street pavement. At the joints the boxes were spliced by 
wooden battens, covered with felt and thoroughly pitched, to exclude 
moisture. After the wooden box was laid, the whole structure was 


THE CONSTRUCTION OF UNDERGROUND CIRCUITS . 143 

thoroughly tarred as an additional precaution against decay. Though 
\ alentine ducts are still used to some extent, experience has demon¬ 
strated that this form of conduit is not suitable for permanent under¬ 
ground structures, especially for those in which lead cables are to be 
placed. The more or less inevitable decay of the wooden box gener¬ 
ates sufficient acetic* acid to initiate chemical action upon the lead 
coating, which is sufficient to destroy the cable within a few months, 
bor other forms of cable, excepting those which are lead-coated, the 
Valentine conduit forms the cheapest device, and one which is rea¬ 
sonably successful for a limited life. 



Fig 90. The Wyckoff or MacDonald Conduit 


166. The Wyckoff or MacDonald Conduit. — This is an attempt 
at a structure slightly more substantial than that of Valentine’s. It 
consisted of a number of circular ducts, as represented in Fig. 90, 
bored in blocks of creosoted wood, the blocks being tongued and 
grooved together in a substantial manner. This conduit could be so 
built that the different pieces should always break joint, and there¬ 
fore the difficulties of unequal settlement of successive lengths was 
avoided. The Wyckoff is laid precisely the same way as the Valen¬ 
tine, and for lead-covered cables is open to the same objections. 














144 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


167. The Paper Conduit. — A conduit involving the use of 
paper tubes has been proposed, consisting of a rectangular wooden 
box in which a number of tubes of pasteboard of the requisite size 
are laid, and the interstices between the tubes filled with asphalt. 
As a result, the pasteboard forms a mold, around which the asphalt 
may be poured, thus forming a block filled with smooth cylindrical 
holes for the reception of the circuits. It is stated that this device 
gives good results. However, there is as yet insufficient experience 
with it upon which to base a conclusive verdict. 



Fig. 91. Iron Pipe in Conduit. 


168. Pipe Conduits. — Four very successful forms of conduit 
depend upon the use of metal pipe, surrounded either on the interior 
or the exterior with a cementing compound. 

hiRST.— Wrought-Iron Pipe in Hydraulic Cement. — This con¬ 
duit is constructed by opening an appropriate trench in the street, 
the bottom of which is covered with a layer of 6" or 7" of good 
concrete. A suitable mixture for this purpose may be made of two 
parts Rosendale cement, three parts sand, and five parts broken stone. 
After the bottom is thoroughly leveled, and the concrete rammed 













THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


145 


into place, being carefully graded, a layer of wrought-iron pipe of 
appropriate diameter to receive the circuits is laid upon the concrete. 
1 hese pipes are jointed by means of vanishing screw thread coup¬ 
lings, making a joint which is absolutely tight. An entire section 
of conduit, embracing the space between two adjacent manholes, 
is laid at one time. As soon as the first layer of pipe is in its 
place, the spaces between and around the tubes are carefully filled 
with concrete, thoroughly rammed into place. Upon the setting of 
this concrete, a second layer of pipe is introduced, and this process 
repeated until a sufficient number of iron pipes are laid to give the 
necessary capacity to the subway. See Fig. 91. 

After the last row is in place, a top coating of concrete, 3" to C" 
in thickness, is spread over the pipe, a layer of plank placed upon 
the top of the concrete to secure the structure against damage from 
the tools of workmen opening the streets, and the pavement re¬ 
placed. This structure makes an excellent conduit in every respect, 
being probably the best one now known. It is water and gas tight. 
It may be built to accommodate at pleasure any number of circuits, 
and is sufficiently flexible to enable reasonable bends between man¬ 
holes to be successfully made; and in cases of streets crowded with 
underground structures, the iron pipe may thread through pr around 
other obstructions in a way impracticable in any other forijn of con¬ 
duit. Experience with this form of subway has shown that in 
process of time the iron pipe may rust away ; but in this event a 
smooth cylindrical hole is left, extending through a solid block of 
concrete, which during the time required for the destruction of 
the iron pipe has become as hard as stone, thus leaving ample pro¬ 
tection for the inclosed circuits. While from a constructive and 
maintenance standpoint, this device presents all the advantages to 
be desired for a conduit, it is quite expensive to build. 

Second. — Wrought-iron Pipe in Asphaltic Concrete. — A sim¬ 
ilar conduit has been proposed, by imbedding wrought-iron pipe in 
asphaltic concrete instead of cement. The substitution, however, 
of the asphalt for the cement concrete possesses no particular advan¬ 
tage, and is still more expensive to build. 

Third. — Zinc Tubing in Hydraulic Cement. — To cheapen the 
iron-pipe conduit, it has been proposed to bed zinc tubing in hydraulic 
cement ; the idea being that economy would be affected by the use 



146 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


of very thin and light zinc tubing, which would be much cheaper 
than the previously proposed iron pipe. The zinc tube was simply 
to serve as a mold around which concrete would be placed; the 
expectation being that the zinc tube, in any event, would certainly 
disappear, leaving the desired hole in the cement. This device, 
however, has not met with success, as the zinc tube, when made 



Fig. 92. Cement-lined Iron Pipe. 


sufficiently heavy to stand the ramming of the concrete, proved more 
expensive than the corresponding iron pipe. 

169. Iourth. — Cement-Lined Iron Pipes. — Another effort to 
cheapen the iron-pipe conduit has resulted in the construction of 
a very thin pipe made of sheet iron into which a layer of cement 
is introduced, surrounding a mandrel, that is subsequently withdrawn, 















THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


147 


thus leaving a continuous tube of cement protected by a thin shell 
of sheet iron, the expectation being that pipe of this description 
would be sufficiently strong to stand laying in the street, and that 
after the pipe was once in place it would be protected from further 
injury by the surrounding concrete and soil. This conduit has met 
with much deserved success, and so far as first cost is concerned, 
is decidedly cheaper than that involving the iron pipe. The appear¬ 
ance and method of constructing a conduit of cement-lined iron pipe 
are shown in Fig. 92. 

170. The Dorset or Callender-Webber Conduit. — This conduit 
consists of tubular blocks some 4 ft. in length, made of asphaltic 
or pitch concrete molded around mandrels of the required size to 



give a number of 3" holes extending entirely through the block. 
See Fig. 93. 

The conduit is constructed by laying, at the bottom of an appro¬ 
priate excavation, a series of the perforated blocks ; the joints being 
made by carefully abutting the ends of successive blocks, and uniting 
them with a mixture of hot asphalt, pitch, or tar. It was found, 
however, exceedingly difficult to align the blocks sufficiently ac¬ 
curately to make the ducts exactly continuous ; and any subsequent 
settlement of the soil caused the conduit to open at the respective 

joints. 

171. The Chenowith Conduit. — The Chenowith conduit was 
an attempt to build between manholes' continuous tubes of cement. 
This was accomplished by making a series of mandrels split Ion- 



















148 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


gitudinally into three parts, held in place during construction by a 
spiral ribbon of sheet iron. A number of these mandrels were 
placed at the bottom of the street excavation, and concrete tamped 
solidly around them. The metal ribbon was lubricated with soapstone 
to facilitate the extraction of the mandrel, and on the withdrawal 
of the mandrel remained in place in the concrete. After the concrete 
is set, the metal ribbon can be pulled out and used again. By this 
means, between successive manholes, a continuous block could be 



Fig. 94. 10" x 10" Terra Cotta Duct. 


constructed having the appropriate ducts to receive the necessary 
circuits. 

172. The Terra-Cotta Conduit. — An exceedingly valuable 
form of conduit, embracing nearly all of the points required for the 
successful protection of electrical circuits, being withal economical 
to construct, has been found in the use of terra-cotta blocks for the 
purpose of forming the subway. A rectangular pipe is made of 

terra-cotta ware about 3 ft. long, having a partition in the center. 
See Fig. 94. 

Successive lengths of this pipe are joined by wrapping the sue- 






THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


149 


ceeding sections with heavy jute dipped in asphalt. The jute wrap¬ 
ping makes a joint which successfully holds the lengths of pipe 
correctly in place, and a thorough application of asphalt ensures a 
joint which is water and gas tight, and does not decay. Care must 
be observed not to apply the asphalt too hot, or the jute will be 
injured. The conduit is formed by placing at the bottom of the 


Fig. 95. Laying 10" x 10" Ducts. 



street excavation the requisite number of earthenware pipe to give 
the desired capacity. It is usual to lay the pipe upon a bed of con¬ 
crete, and to protect it on either side and on the top by a concrete 
wall 4 to 6" thick. Conduits of this class have been constructed 
to a large extent, and so far have proved eminently successful. The 
chief objection to this style of construction is found in the fact that 








150 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


the earthenware pipes are so designed as to accommodate several 
cables in one duct. While there is little or no difficulty in introdu¬ 
cing several cables into one division, it is often exceedingly difficult 
to withdraw them after they have been in place any length of time 
without destroying the sheath. The operation of introducing the 
10" X 10" terra-cotta pipe is shown in Fig. 95. 

173. Terra-Cotta Separate Duct System. — To overcome the 
difficulty in withdrawing cables, which is experienced in 10" x 10' 
ducts, an earthenware conduit has been devised, which consists of 
a number of blocks of earthenware pipe, each having a separate 



Fig. 96. The Terra-Cotta Separate Duct System. Pipe Sections. 


duct. These blocks are 5" square, and from 18" to 2 ft. in length. 
They are made of earthen pipe, having the general appearance in¬ 
dicated in Fig. 96. 

To construct a subway out of this material, an appropriate street 
excavation is made, the bottom of which, after having been carefully 
graded, is lined with a layer of 6" of concrete. Upon this concrete 
the earthenware ducts are built, in precisely the same fashion as 
a brick wall is laid up. To secure proper alignment, it is customary 
to lay one line of duct through the center of the trench, to guide 
the alignment of all the succeeding layers of pipe. As the work 






THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


151 



Fig. 97. The Separate Duct Terra-Cotta Conduit. 




152 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


progresses, mandrels some G or 8 ft. in length, which closely fit the 
ducts, are placed in each row of pipe, thus ensuring correct align¬ 
ment, until the cement in which the pipes are laid has had a chance 
to set. As fast as the subway is built, the mandrels are pulled along, 
thus keeping the pipe constantly in true line. 

Conduits of this description should be constructed by laying the 
pipe up in a strong mixture of either Rosendale or Portland cement. 
The joints in the pipe should be hammered down so as to be as close 
as possible, and not to exceed J". As all the pipe in burning is 
slightly concave, care should be taken to lay the subway with the 
convex sides upward in every instance, so that no obstacles may be 
experienced in the subsequent introduction of the cables. As the 
ducts are laid, all the joints between the successive blocks should be 
thoroughly grouted with cement. This form of conduit presents 
the advantage of great flexibility ; as a subway of any number of 
ducts can be formed, and, in order to accommodate street obstruc¬ 
tions, the geometrical cross-section of the conduit can be varied at 
pleasure. After completion, a scraper, similar in shape to a boiler- 
tube cleaner, should be drawn through each of the ducts, which serves 
to cut away and clean out all gravel and cement which has found its 
way accidentally into the ducts, and then by washing the ducts with 
a stream of water from a hose, a clean, polished hole is obtained, ex¬ 
tending between the adjacent manholes. While this form of conduit 
is slightly more expensive than rectangular earthen pipe, it presents 
the inestimable advantage of giving a separate duct for each cable. 
The method observed in building this form of conduit is seen in 
| Fig. 97. 

174. The Crompton System. — The subways so far considered 
have been only adapted to the use of highly insulated cables, as the 
designs have been such as to afford no insulation to the circuits. 
Several European attempts have been made to construct a subway 
in which bare copper conductors could be used, thus avoiding the 
expense of insulated conductors. Notable among these systems is 
that of Crompton, which has received quite an extended development 
in London, Nottingham, and Birmingham. In the Crompton system 
the conduit is usually laid under the foot-walks, and not under the 
street proper, as is customary in this country. The construction 
involves the excavation of a trench, which, for the ordinary sized 


THE CONSTRUCTION OF UNDERGROUND CIRCUITS . 


153 


conduit is about 3 ft. 5" wide, by 1 ft. 9" deep. This trench is then 
supplied with a bottom and side walls of concrete, the bottom being 
about 3" in thickness, while the sides are from 6" to 8". At inter¬ 
vals of about 50 ft., so arranged as to be opposite every alternate 
house, a handhole cover is introduced, to give access to the conduit 
for the purpose of* taking out service wires. Directly under this 
handhole a heavy rectangular piece of oak timber is set in the con¬ 
crete sides of the subway. Upon this timber the requisite number 
of porcelain insulators are placed to carry the circuits for which 
the conduit is intended. These insulators have a simple slot on 



Fig. 98. Crompton Conduit, Half Plan and Section at Handhole. 


their tops in order to receive and carry the lines, that are merely 
naked strips of copper. Fig. 98 indicates a half-plan and half-section 
of the conduit at a handhole. At intervals of about 300 ft. the 
handholes are made quite large in order to afford the necessary 
room for stretching the copper strips. The subway is completed by 
placing the requisite iron casting at each of the handholes, and by 
covering the entire top of the trench with a layer of Yorkshire flag¬ 
ging, after which the paving of the foot-walk is replaced, the only 
indication remaining being the handhole covers at the houses. The 
circuits consist of copper strips about thick, and from to lj" 
wide. The conductors are introduced by running a cord between 






































































































154 THE ELECTRICAL TRANSMISSION OE ENERGY. 

the successive handholes, and then joining the copper strips in 
continuous lengths and hauling them in. 1 he hauling cord is in¬ 
troduced by attaching it to the collar of a small dog, who is trained 
to run along the bottom of the subway from handhole to handhole. 
At each handhole cover an inspector is stationed who sees the copper 
ribbon is placed in the slot of the insulator as it makes its appear¬ 
ance. When a length of 300 ft. of copper ribbon is introduced, one 
end of it is made fast in the end insulator, and then by means of a 
hydraulic jack, the ribbon is pulled up to the appropriate tension, 

1 



Fig. 99. Crompton Conduit, Longitudinal Section. 


and secured at the other end in a similar insulator. The method 
of joining and securing the strips is indicated in Fig. 99. 

Here it will be seen that there are two sets of heavy oak blocks 
(SB) set in the concrete. On these blocks the insulators (I) rest, 
and carry clamp (S), that by means of set screws (W) tightly pinch 
and hold the copper strips in place. A pad of rubber (R) distributes 
the pressure equally over the insulator and prevents cracking the 
porcelain. This structure certainly seems to present a maximum of 
advantage in the way of small street space occupied, ease and econ¬ 
omy of construction, and flexibility and convenience for rearrange¬ 
ment or extension of circuits. The English reports are so satisfactory 
that it seems strange that similar devices are not tried in this country. 

















































































































THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


155 


175. The Brooks System. — This system, the invention of David 
Brooks of Philadelphia, embodies the use of a heavy mineral oil, one 
of the best insulators known. Mr. Brooks’s invention consisted in 
placing in a trench, excavated under the pavement, an iron pipe of 



i 

I 

Fig. 100. Brooks System Junction-Box. 

sufficient size to carry the necessary conductors for the system. 
Occasionally a rectangular box is introduced, as shown in Fig. 100, 
into which each end of the pipe opens by means of a flanged joint. 
This box serves the purpose of affording an opening into the pipe 



of Cable and Oil Pipe. 

through which the conductors could be drawn in. At various inter¬ 
vals a service-box, as shown in Fig. 101, is introduced, by means of 
which distribution could be accomplished. The cables used in the 
Brooks system consisted of solid or stranded copper conductors, 
shown in section in Fig. 102, covered with a layer of raw jute or 
hemp, to prevent contact between the conductors, or grounding 





































































156 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


on the iron pipe. This covering was placed on the outside of the 
conductors by a braiding-machine, and then the cable drawn into 
the pipe through the service-boxes. As soon as the conductor was in 
position the pipe was filled with boiling resin oil, which formed the 
insulating material, and preserved the electrical qualities of the cable. 
While in some instances the Brooks system has been found to stand 
up admirably under severe tests, considerable difficulty has been ex¬ 
perienced in keeping the pipe sufficiently tight to retain the fluid 
insulator. For electric lighting service the Brooks system has in 
some instances given fair satisfaction ; yet its largest use has probably 



Fig. 103. Johnstone System. 


been found in telephone and telegraph work, and for this purpose it 
has not fulfilled expectations, as much of this conduit which has been 
introduced has, after a time, been found gradually to fail in insulation. 

176. The Johnstone System. — The Johnstone conduit system 
bears evidence of exceedingly careful design, the structure having 
been planned to meet all exigencies to which subways are called to 
respond. The arrangement consists of a series of cast-iron troughs 
made in lengths of about 6 ft., so designed in sections that a con¬ 
duit of any desired capacity can be built. The sections, as shown in 
the illustration, Fig. 103, are arranged to comprise a series of rect¬ 
angular ducts, into which the circuits may be at any time placed by 




































THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


157 


drawing in cables in the ordinary way. At frequent intervals a 
service-box is arranged upon the top of the upper row of ducts, out 
of which appropriate leads can be taken to serve the desired installa¬ 
tion. At the street corners iron manholes (Fig. 104) are introduced, 
into which the ducts end, and from which all rearrangements or con¬ 
nections can be made. While this conduit is admirable in every 



Fig. 104. Manhole of Johnstone System. 


respect, it is one of the most expensive forms of subway constructed ; 
its cost being so great as to almost prohibit its use. 

177. The Kennedy System. — The Westminster Company of 
London have employed a modification of the Compton conduit, de¬ 
signed by Professor Kennedy, that has given good satisfaction. A 
general idea of this method may be obtained from the accompanying 
illustration, Fig. 105, showing a cross-section of this conduit de¬ 
signed to carry two lines of main feeds, and a three-wire distributing 
system. A trench is excavated in the street, which, in a manner 













































































































































































































































158 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


similar to that of the Compton construction, is lined on the bottom 
and sides with concrete. The conductors, as in the Compton system, 
are bare copper strips ; but instead of being supported upon insulators 
set in oak blocks, the insulators are solid porcelain supports, which 



Fig. 105. Section of Kennedy System. 


are set directly in the concrete bottom. The top of the conduit is 
covered with flagging or iron casting. The circuits, formed of bare 
strips of copper wire, are drawn through the conduit, being placed in 
the insulators by means of handholes in a manner similar to that 
adopted by the Compton system. 



Fig. 106. St. Janies System. 


178. St. James System, London. — This arrangement is very 
similar to that of the Compton and Kennedy systems. The conduit, 
however, instead of being formed of concrete, is made of an iron trough, 
Fig. 106, set at the bottom of the street excavation, thus avoiding the 


























































































THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


159 


use of cement, and greatly expediting the street work. This trough 
is provided with a water-tight cover, secured by means of bolts and 
packing. At frequent intervals throughout the trench, a porcelain 
bridge is placed for supporting the circuits, which consist of bare 
copper strips set on-edge, or stranded cable, and strained to be suffi¬ 
ciently taut to remain in a straight line. It is obvious that in all of 
the systems where bare wire mains are employed, special precaution 
must be taken to insure careful drainage, so that all incursions of 
moisture from the street may be readily and quickly removed in 
order not to flood the mains. 



Fig. 107. Parisian System. 


179. The Parisian Systems. — A large part of the under¬ 
ground distribution of Paris has been accomplished by the use of 
bare conductors extended through concrete trenches in a manner 
similar to the London system. The subway is formed by exca¬ 
vating a trench under the sidewalk, which is lined with concrete 
on the sides and bottom, having a flagstone, or similar covering, 
placed over the top (Fig. 107). The cables are almost universally 
bare stranded copper wire. They are carried through the trench, 
being supported upon porcelain insulators, carried upon iron pins 
set and secured in the concrete forming the bottom of the trench. 
In many of the German and Italian cities similar methods of 








































160 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


distribution have a widespread introduction, and are successfully 
operated. 

180. Inflexible Systems. — The examples of subway systems 
so far cited appertain exclusively to the flexible system, that, owing 
to its greater adaptability to service fluctuations, has deservedly 
obtained a more widespread development. In the succeeding illus¬ 
trations the inflexible system is presented. Numerous modifications 
of the methods here given will readily occur to the facile designer, 
in order to adapt this principle to the varying circumstances of 
particular localities. 

181. The Callander Solid System. — By the Callander solid 
system a series of cast-iron troughs are arranged along the bottom of 
a trench excavated in the street. In the troughs the requisite number 

of cables are extended, supported from 
time to time upon insulating pieces fixed 
in the troughs. This protection is found 
to be necessary, from the fact that the in¬ 
sulating compound, with which the trough 
is to be filled, is never absolutely hard, but 
behaves like a very viscous fluid; and if 
the cables were unsupported they would 
gradually settle, and ultimately lie upon 
the cast iron forming the exterior of the 
subway, thus short-circuiting, and spoiling 
the entire structure. The cables are usu¬ 
ally stranded copper rope of the appropriate size, covered with an 
additional insulating compound. In view of the melted asphalt, or 
insulating compound, which is subsequently poured in, this would 
seem unnecessarily expensive, as bare copper conductors thus ar¬ 
ranged would answer equally as well. After the cables are in place, 
the entire trough is filled with Trinidad asphalt, thus completing 
the structure, and presenting an appearance as indicated in Fig. 108, 
in cross-section. 

The troughs are laid in lengths of 6 ft., and are of about ^" in 
thickness, a cast-iron cover being placed over the top to protect the 
conduit from injury. At appropriate intervals manholes are intro¬ 
duced (see Fig. 109). 

The design of manhole adopted by the Callander system is one to 



Fig. 108. Cross-section of the 
Callander Solid System. 


















THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 161 


afford the greatest possible protection to the circuits. As indicated 
in Fig. 109, the manhole consists of an excavation below the street 
level, into which is set an iron chamber surmounted with a water¬ 
tight cover, which is screwed down and rendered moisture-proof 
by being bolted to a rubber gasket that sets upon the top of the 
manhole casting. The mains contained in their trough of asphalt 
are carried through the iron walls of the manhole and carefully 



Fig. 109. Manhole, Callander Solid System. 


cemented into place. The service mains are in a similar manner 
carried out through a hole drilled into the manhole wall, and through 
a packed joint that is moisture-proof. The cast-iron box forming the 
manhole is set inside a cemented chamber that is so arranged as to 
be entirely surrounded by an air-space, into which drainage may 
accumulate, and be conducted away by appropriate connection to the 
sewer. While the Callander system presents a very perfect form of 
underground service, the iron trough carrying the cable seems an 
unnecessarily expensive precaution. 












































































162 


THE ELECTRICAL TRANSMISSION OE ENERGY. 



182. Two forms of cheaper construction are indicated in Figs. 
110 and 111. The arrangement shown in Fig. 110 is that which is 
adopted in the distributing systems in Cologne and in two or three 
other European cities. The arrangement consists of a wooden box, 
shown in cross-section, into which a carefully insulated concentric 

cable is placed, being suspended at 
intervals of every few feet by means 
of an iron stran. After the cable is 

j. 

laid in place, the box is poured full 
of asphalt, or concrete, thus entirely 
surrounding the cable with an insu¬ 
lating material. The asphalt and the 
box serve to protect the cable from 
injury in the street. Installations of 
this description have given good ser¬ 
vice, though they have, as yet, not 
been in operation sufficiently long to 
determine their probable life. It is 
necessary to use a very 
carefully prepared cable, 
as is indicated in the illus¬ 
tration. The cable is con¬ 
centric, the outer conduc¬ 
tor of which is protected 
by two lead sheaths and 
an iron armor. The ex¬ 
terior layer is of tarred 
hemp. It will also seem 
that an installation of this 
kind, made and protected 
by only a wooden box, would be subject, sooner or later, to the 
decay of the woodwork. 

As an improvement both in durability and economy, the con¬ 
struction indicated in Fig. Ill has been adopted in Zurich. The 
cable is a concentric conductor, insulated with paper, and having a 
lead sheath separating the inner and outer mains. The conduit 
consists of an earthenware trough placed just beneath the pavement 
level. It is strong, simple, cheap, can be rapidly laid, and affords an 



IRON HOOK 


WOODEN TROUGH 


ASPHALT 


Fig. 110. Cologne Conduit. 




















































































































THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 163 


excellent mechanical protection to the cable. It is made in sections 
of 3 ft. in length, and, if carefully placed in the street excava¬ 
tion, requires only a little grouting at the joints. The cables are 
simply laid at the bottom of the earthenware trough, which is then 
filled with sand, and completed with an earthenware cover. Some 
18 miles of this conduit, containing 60 miles of cable, are in active 
operation. 

183. Manholes. — It is essential, at frequent intervals, to pro¬ 
vide means of access to underground conduits for the introduction or 
rearrangement of circuits, for distribution, and for such changes in 
direction of the subway as the location of streets renders essential. 
Such opportunities for access consist in chambers, constructed under 
the pavement of the streets, of sufficient size to allow reasonable 
room for two or three men to work. Usually these chambers are 



Paper Lnsulation 


Outer Conductor 
* 6 * 


Two Lead 
Sheath Coverings 

_ 



Inner Conductor 
Stranded Copper Cable 


Inner Lead 
Sheathing 


Outer Paper Insulation 


m§m 

m mml 


: n. 


'HE 




Double Covenng of 
Jute over all 


Fig. 7 7 7 . Zurich Conduit. 


rectangular vaults, built of either concrete -or brick. They are 
roofed over, either with arches or structural iron carrying an arch 
brick, and provided with an iron frame supporting the manhole 
cover. The various branches of the conduit are arranged to extend 
through the walls of the chamber, giving free access to all of the 
ducts converging at the particular manhole. It is advisable to con¬ 
struct the manholes of ample dimensions ; for while, by increasing 
the size of the chamber, the initial cost of the underground system 
is slightly augmented, yet the future expense entailed in introdu¬ 
cing the circuits, and the labor constantly necessitated by the re¬ 
arrangement and maintenance, is so much decreased by affording 
to the workmen a reasonable amount of space in which to perform 
their avocations, that the extra capital invested is usually found to be 
well expended. 

A vault 5 ft. wide by T ft. long, and from 4 ft. 6" to 6 ft. high, 
is as small as should be designed for large underground systems, 























164 


77IE ELECTRICAL TRANSMISSION OF ENERGY. 


where considerable splicing and rearrangement of circuit is to be 
expected. 

Inasmuch as the manholes are the lowest points of the sub¬ 
way, it is essential to provide for drainage, by connecting the 
bottoms of each of the vaults with the sewers, by the means of 
an ample drain-pipe provided with a catch-basin and trap. If 



Fig. 112. A Terminal Manhole. 

precautions of this kind are omitted, it frequently happens that 
in heavy rainfalls the conduit becomes flooded, and the circuits 
much injured. This provision is of paramount importance in sub¬ 
ways containing uninsulated circuits. If lighting circuits are rea¬ 
sonably convenient of access, it is well to arrange in the vaults 
provision for incandescent lamps, as by this means workmen are 
afforded reasonable illumination for the prosecution of their work, 


























THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


105 


and all of the dangers attendant upon lanterns, or other methods 
of lighting, are avoided. While the manholes are in use by the 
workmen, it is necessary to provide some method of protection 
to prevent travel in the street from being injured by falling into 
the manhole, and also to prevent injury occurring to the workmen 
from causes of this kind. It is common to arrange a circular iron 
pipe guard, so designed as to be readily folded up. The guard 
can be unfolded and secured by setting inside the iron ring forming 
the manhole ; and then a suitable red flag, lantern, or other signal 
can be attached in order to call the attention of the passer-by to 
the fact that the street is open at these points. 

As an example of manhole construction, Fig. 112 is from a 



I _d__ 

Fig. 113. New York Subway Manhole. 


photograph of the terminal manhole of a large underground sys¬ 
tem. The subway may be seen entering the wall of the manhole, 
the lower rows of ducts being filled with cables that in the fore¬ 
ground turn and run upward into the station above. 

As additional illustration, the vault of the Johnstone, Fig. 104, 
a splendid but expensive device, and that of the Callender Solid 
System, Fig. 109, may be consulted. 

The typical manhole adopted for New York subways, arranged 
for high tension current distribution, is shown in Figs. 91 and 113. 
In Fig. 113 the cross-section of the construction is shown, indi¬ 
cating a brick or iron chamber, into which the iron-pipe ducts 
open. Special attention is given to the method of securing the 
cover in order to hermetically seal the chamber. The device con- 

























































106 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


PTT r:i 


sists in a heavy iron frame carrying two covers — an inner and 
an outer cover. The inner cover rests upon an elevated ring • 
tightness being secured by means of a circular cylindrical gasket ; 
the cover being forced into place by means of the screw b, and 
cross-piece b'. Drainage is secured by connecting the gutter 
formed by the elevated ring to the sewer by means of the pipe P. 
The structure is completed by the addition of the street cover. 

i The perspective view of 

this method of construc¬ 
tion is shown in Fig. 91, 
wherein the arrangement 
for aiding the ventilation 
of the subways by means 
of a large air-pipe placed 
parallel to, and in the same 
trench with, the ducts, will 
be noted. The air-pipes 
extend from the blower 
stations and connect with 
the various manholes ; 
maintaining throughout 
the subway system a pres¬ 
sure slightly in excess of 
that of the atmosphere, 
thus preventing the in¬ 
gress of gas. 

184. Junction-Box for 
Underground Railway 
Feeds. — A large system 
of underground distribution has recently been installed in Phila¬ 
delphia, in connection with the substitution of electricity for animal 
power upon the street railway lines. 

The conduits consist of cement-lined iron pipes, set in concrete. 
The main subway from the station consists of eight pipes, three 
inches in internal diameter, laid two feet deep, and intended each to 
carry two No. 0000 lead-covered cables. The manholes are placed 
at suitable distances, to enable careful and efficient handling of the 
wires, and to allow the railway company to make any combination 



plug! 

HARD RUBBER'' 




Fig. 114. Street Railway Junction-Box. 













































THE CONSTRUCTION OF UNDERGROUND CIRCUTTS. 167 


or rearrangement of the circuits of the different streets, as may be 
found advisable. The accompanying illustration, Fig. 114, includes 
the design of a manhole which has been worked out in admirable 
fashion for this purpose. 

A circular iron chamber is arranged, carrying six inlets, some 
thing in the shape of a six-point star. Each of the inlets consists 
of a stuffing-box, through which the cable is introduced into the 
interior of the manhole by means of a water-tight joint, to which 
the duct of the subway is hermetically attached. All of the cables 
thus open into the box, and may obviously be arranged or changed 
in any desired manner. The cover of the box is firmly locked in 
place by means of bolts and a water-tight gasket. 

185. Introduction of Circuits. — After the completion of the 
underground structure, the introduction of the circuits becomes a 
matter for consideration. This is accomplished by the process of 
“rodding.” The workmen are supplied with a number of light- 
jointed pine sticks, about J" in diameter, and from 3 to 4 ft. in 
length. These rods are equipped with a screw or bayonet joint at 
either end, that they may be successively jointed together in series. 
Upon entering the manholes, the operator proceeds to connect up one 
or two lengths of these sticks or rods, and pushes them through the 
duct of the subway, into which it is proposed to introduce the circuit. 
By successive additions to the rod, it may be thus shoved entirely 
through the duct into the next adjacent manhole. Connection is thus 
obtained between the two manholes, whereby a rope or wire may be 
extended through the duct. As soon as this is accomplished, the 
reel upon which the conductor is wound is placed over the opening 
into one of the manholes, and cables lowered into the vault around 
a large-sized sheave or pulley, and introduced into the duct. The 
cable is then attached to the rope, and hauled through the duct from 
one manhole into the next one ; the necessary traction being sup¬ 
plied by means of a fall and windlass located at the farther vault. 
Thus length after length of circuit may be introduced, until the 
entire quantity is laid. The different lengths may be then spliced 
so as to form a continuous circuit. 

186. Pneumatic Rodding. — Where it is desired to rod a num¬ 
ber of ducts extending between two adjacent manholes, the process 
may be very greatly facilitated by the recently devised method of 



168 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


“ Pneumatic Rodding.” The workmen in one manhole are furnished 
with a “dart,” which is a spool-shaped piece of wood about six inches 
long, having a leather washer on each end, arranged to make the 
dart fit tightly into the ducts. The rear end of the dart carries a 
ring to which a light cord is attached, loosely coiled on the bottom 
of the manhole. At the more remote manhole, the workmen are 
provided with an air-pump capable of being fitted over the mouth of 

the duct. The dart being placed on the mouth of the duct, a few 

/ 

strokes of the air-pump produce sufficient vacuum to cause the dart 
to fly swiftly through the duct, dragging the cord after it, a few 
seconds of time being all that is required to perform the operation. 

187. Gas. — Perhaps the greatest danger to which underground 
subways are exposed is the accumulation of illuminating gas, either 
in the ducts or in the vaults. The pipes forming the gas-plants, 
ramifying through the streets of all the larger towns, are usually 
constructed of cast iron, which permits a considerable leakage of 
gas directly through the material of the pipe itself. In addition 
to this, the leaky joints and service-pipes are sufficient to completely 
impregnate the soil of the streets with illuminating gas. In fact, 
the statistics of some cities show that the gas companies are un¬ 
able to account for some 15 to 20 per cent of the gas manufac¬ 
tured by them, this loss being almost entirely ascribed to street 
leakage. The vaults and ducts of the subways form convenient 
places for the accumulation of the gas, which collects in them by 
percolating through the soil. In the early days of subway construc¬ 
tion, many serious accidents happened, either from asphyxiation of 
the workmen entering the vaults for the purpose of drawing in, or 
making changes in, the circuits, or from veritable explosions in the 
subways, due to the gas forming explosive mixtures with the atmos¬ 
phere, and chancing to ignite from some accidental spark. To 
obviate casualties from this cause, it is now customary to provide 
all of the important subways with means of ventilation, two plans 
having been adopted which have proved fairly successful. 

First, -r— The least expensive method consists in grading each 
subway between adjacent manholes, so that the ducts shall have a 
slight fall from one manhole to the next. In order to provide for 
a reasonably uniform grade throughout the entire subway, sections 
between the manholes can be arranged so that two adjacent sections 


THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


169 


grade into the manhole, and the next two grade azrny from the man¬ 
hole. Then, if the cover of the vault is arranged with suitable 
openings, so as to provide a chance for the entrance of air, it is found 
that the subways will keep fairly pure, in cases where the gas leak¬ 
age into the soil is not too rapid or excessive. 

Second. — The method of ventilation which is perhaps the surest, 
although the most expensive, requires the installation of one or more 
ventilating plants at various points along the subway. Under these 
circumstances no particular attention need be paid to grading the 
conduit, excepting for purposes of drainage ; and the vault covers, 
instead of being rendered open to the atmosphere, are made as 
nearly air-tight as is practicable. At the ends of the subway, or 
if the length of the underground construction requires it, at several 
intermediate points, ventilating plants are arranged, consisting of air¬ 
blowers driven by some form of prime mover, which constantly forces 
into the subway quantities of fresh air. At first sight it would seem 
as if it were essential to keep a steady flow of air through the sub¬ 
way, in order to clear the ducts of the accumulation of gas; but, on 
the contrary, the attempt of the ventilating plant is to produce a 
pressure in the subway which is a little greater than that of the 
atmosphere. Under these circumstances the incursion of gas into 
the subway is prevented from the mere fact that the pressure there 
being greater than that of the exterior atmosphere, causes the gas 
to flow away from and not toward the subway. Under these circum¬ 
stances, the air which is forced in finds a natural outlet through the 
porosity of the soil itself. 

188. Electric Railway Conduits. — The extension of the elec¬ 
tric railway is proving one of the most important factors in electric 
distribution; and probably this method of propulsion would have 
attained a still greater expansion could some successful, and at the 
same time economical, form of substructure be devised which would 
relieve city streets of the overhead conductors that are essential to 
the trolley system. Long since the railway feeds were placed under¬ 
ground, either by means of armored insulated cables, or, more eco¬ 
nomically and equally successfully, by placing bare wire mains in 
wooden conduits insulated with asphalt, after the fashion of the 
Callander Solid system. There yet remains the trolley wire, which 
so far may be practically said to have resisted all attempts at removal. 



170 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


Many extensive and expensive experiments have been tried with vari¬ 
ous forms of underground structures, intended to carry the trolley 
conductor beneath the surface of the street. Generally speaking, 
these attempts may be so far stated to have been failures ; for the 
difficulties encountered in securing requisite insulation, providing for 
surface drainage, and allowing successful contacts with the motors, 
have been too great for inventors entering the field. In favorable 
locations it is undoubtedly possible to construct a successful street 
railway substructure, yet the additional expense of the conduit is so 



Fig. 115. Details of Buda-Pesth Conduit. 


great, and the advantages to be derived from its use so few, that little 
or no headway is likely to be made in this direction as long as the 
remotest possibility exists of obtaining an overhead franchise. Three 
or four electric roads in Europe, and perhaps as many more in this 
country, are running upon underground systems ; but as yet the 
electrical railway conduit has hardly transcended the experimental 
stage. 

189. The Buda-Pesth Conduit. — The line at Buda-Pesth was a 
pioneer European experiment. The mechanical details are indicated 
in Fig. 115, from which it will be seen that the construction resem- 

















































THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 171 

bles a cable road design, the conductors being angle bars supported 
on the yokes, as at B. The Blackpool conduit is shown at A, Fig. 
115. The conductors are copper bars, as at FF, supported on 
special insulators attached to each side of the conduit. The details 




of these are shown at P, and a general view of the track at C. 
From the car the device for contact is a bar extending through the 
slot, carrying two shoes pressing on the conductors. 

190. The Waller and Manville System. — This is constructed 
as shown in Fig. 116, the upper illustration indicating the arrange¬ 
ment where a single conductor is used, while the lower one gives the 





































































































































172 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


design for a metallic circuit. The conduit consists of a rectangular 
cement trough placed under the rails. On the under side of the 
roof a series of insulators is suspended carrying peculiar projecting 
arms FF. The conductors are heavy copper rods that nominally lie 
upon the supporting projections FF. The plow or trolley hangs 
from the car by means of a bar passing through the slot between the 
rails, and is adjusted at such a height as to run clear of the insulators 
FF. The trolley carries triangular grooves which engage the copper 
conductors, lifting them off the insulators in much the same fashion, 



Fig. 117. The Love Conduit. 

as it runs along, as the grip of a cable car raises the cable from its 
supporting sheaves. 

191. The Love Conduit. — In this country two pieces of rail¬ 
way conduit have been constructed by the Love Electric Traction 
Company, one in Chicago and one in Washington. These experi¬ 
ments are reported to be giving fair satisfaction. The general plan 
of the conduit is seen, from Fig. 117, to be modeled after the usual 
cable railway design. 

The yokes are of cast iron, spaced about every 4 ft., and weigh 
260 lbs. each. They are mounted on concrete foundations ; and 
concrete is employed about the sides of the conduit, the lining 
being of cast iron. The depth of the conduit is 20", and it has a 








THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 173 


maximum width of 14". The width of the slot is The rails 
are grooved, weigh 6d lbs. to the yard, and are bolted directly to 
the yokes. The slot rails are of an inverted U shape, and have 
a long lip or flange extending into the conduit, which protects the 
conductors from water and other debris which might fall into the 
conduit. The manholes are located every 100 ft., being drained by 
6" pipe. A complete metallic system of conductors is used. The 
conductors are of hard-drawn copper, |" in diameter, and are sup¬ 
ported by a special type of insulator, and protected from accidental 
grounding by water, etc. The conductors are made in sections, of 
wires connected every 500 ft. by couplings which allow for contrac¬ 



tion and expansion. They are supported from the yokes by clamp 
insulators, which fit into longitudinal grooves on each side of the 
conductors, making an uninterrupted surface on the under side of 
the latter for the trolley wheel. The trolley or plow, shown in the 
illustration, carries two wheels which run along the under side 
of the conductors. Each wheel is mounted on a swinging bracket, 
and is held against the conductor by a spring, so that a perfect con¬ 
nection is secured. 

192. The Lenox Avenue Conduit. — As indicative of the prob¬ 
able development of the electrical railway conduit, Fig. 118 is a 
























































































































































174 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


cross-section of a conduit which it is proposed to place on Lenox 
Avenue, New York City. The cable railway type of construction is 
proposed, consisting of yoke frames embedded in concrete. The 
conductors are channel irons, and are supported upon a series of 
soapstone insulators set in the manholes, which are reported to be 
placed every 30 ft. along the road. Contact is made with the 
channel iron conductors by means of a plow carrying two rubbing 
contacts that bear upon the conductors. 

193. Metallic Conduits and Cable Sheaths for Alternating- 
Currents. — With the extending tendency to transmit energy by 
means of alternating currents, the question of the effect of metallic 
sheaths for conductors, or metallic structures for conduits, assumes 
considerable importance. Lead and iron are the only metals that 
have so far been used for this purpose. The impedance to which any 
alternating current is subjected, is greatly affected by the magnetic 
permeability of the medium surrounding the conductors ; and also 
depends upon the mechanical disposition of the media. Conductors 
which are sheathed with metal so disposed as to form a closed circuit 
have the impedance factor largely increased. Iron sheaths still fur¬ 
ther augment it. If all the constants of a circuit are known, it is 
possible to calculate the impedance ; but the value of many of the 
factors, however, is still quite uncertain. Some French experiments 
upon lead-covered cables and currents at a frequency of 100 per 
second show the conductors to be subjected to a loss of energy 
varying from 1 to 2 per cent. With iron sheaths, from 5 to 10 per 
cent loss is reported, with one extraordinary instance of a 35 per cent 
loss. While this subject needs much more investigation, it is cer¬ 
tainly safe from present appearances to relieve alternating circuits 
from the presence of metallic surroundings. 


THE CONSTRUCTION OF UNDERGROUND CIRCUITS . 


175 


CHAPTER IV.— Continued. 

THE CONSTRUCTION OF UNDERGROUND CIRCUITS. (Continued) 

PART II. —CABLES AND CONDUIT CONDUCTORS. 

Art. 194. Conduit Conductors. — For all underground circuits, 
excepting such as are designed to go into conduits arranged for bare 
conductors, some special form of insulation is essential in order to 
maintain the electrical integrity of the circuits. To accomplish this 
end, various designs, leading toward the formation of the conductor 
into cables, have been invented. 

195. Armored Cables.— The Siemens Cables. — The earliest 
attempts toward the construction of underground circuits consisted 
in the mere excavation of a trench through the street, into which 
the insulated cable, carrying the distributing circuits, was placed. 
Experience demonstrated that it was difficult to build a cable with 
sufficient mechanical strength to be self-protective against destruc¬ 
tive influences constantly at work to cause the deterioration of street 
structures. Even the best armored cables are liable to be ruined by 
a single stroke of the pickax ; so additional precaution was needed, 
thus causing the development of the more modern types of sub¬ 
way structures. The armored cable, however, is by no means to be 
despised as a method of underground distribution. On the con¬ 
trary, the entire system adopted by the Siemens Bros, is based upon 
a superior construction of the cable (provided with ample protection 
against damage), laid directly in trenches excavated under the pave¬ 
ment in the street. The Siemens cable is of the concentric type ; 
that is, the two conductors forming the circuit are not laid side by 
side, but are arranged one inside the other, separated by the appro¬ 
priate insulating material. Two advantages accrue from this method 
of construction, one being a notable saving of space, insulating mate¬ 
rial, and cost of manufacture, and the other the practical impossibility 
of forming a short circuit with any exterior object, thus affording 
an immunity against fire risks or injuries to workmen. Three of 




176 


THE ELECTRICAL 7RANSMISSL0N OF ENERGY 


the most valuable forms of concentric cable are shown in Figs. 119, 
120, and 121. 

Cable No. 1, Fig. 119, is used by the electric light installations 



Fig. 119. Siemens Incandescent Light Cable, Paris. No. 1. 


in the Theater du Chatelet, and the Opera Comique, Paris. This 
cable has a central conductor of 61 wires, each of three millimeters 



Fi j. 120. Edison Cable, Paris. No. 2. 


in diameter, separated by a layer of rubber five millimeters C 3 g of 
an inch) in thickness, outside of which is placed a surrounding con¬ 
ductor composed of 22 strands, each of 7 wires, 1 T 7 ^ millimeters in 




















THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


ITT 


diameter. A second coating of india-rubber, covered with a lead 
sheath, completes the cable. 

Cable No. 2, Fig. 120, is the cable used by the Secteur Edison 
in Paris, that, in addition to the concentric conductors and lead 
sheath, is provided with a steel wire armor. 

Cable No. 3, Fig. 121, is a special cable used by the Siemens 
Bros, on the five-wire system that they have established in Paris. 

1 and 2 are the concentric conductors ; 3 the balancing main, 
to which allusion will be made in the chapter on paiallel distri- 



Fig. 121. Siemens Concentric Cable. No. 3. 


bution ; a, b, and c insulation ; B lead covering ; J jute; A asphaltum 
insulation ; and E iron armor. 

The mains are laid by merely excavating a trench in which a bed 

of sand is placed for the reception of the cable. 

The methods of making service connections are indicated in Fig. 
122, being very similar to the Edison system adopted in this coun¬ 
try. In order to protect the cable from excavators, it is customary 
to lay directly over the mains a layer of plank or a length of lion- 
wire netting. While the iron-wire netting may call the attention of 
the excavator to the presence of the structure beneath him, the 
















































































































































178 


THE ELECTRICAL TRA NS MI SSL ON OF ENERGY. 


plank is found to be by far the most sufficient protection, inas¬ 
much as it actually prevents pick or shovel from cutting through 
and coming in contact with the cable. 

196. The Edison System. — Under this system, bare conductors 
are inclosed in an iron pipe, protected by an insulating compound, 
the iron pipe having ample strength to protect the circuits from 




Fig. 122. Junction-Box for Siemens Cable. 


external injury. The Edison circuit is formed by inclosing in a 
16-ft. length of iron pipe, about 3" in diameter, three copper con¬ 
ductors of appropriate size. These conductors are separated from 
each other by winding each one with a loose spiral of jute or cotton 
yarn of sufficient thickness to insure the separation of each individ¬ 
ual rod from any of its neighbors, and from the exterior pipe. The 
three copper rods, after having been wound in this fashion, are 
bundled together, and slipped inside of a length of iron pipe. When 























THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


179 


the rods are in position the pipe is poured full of a melted special 
insulating compound, that, on cooling and hardening, holds the con¬ 
ductors firmly in their place. As soon as the insulating material 
has hardened, the completed section of pipe, with its three con¬ 
ductors, is carefully tested, and, if found satisfactory, becomes a 
complete section. All of the Edison underground plant is planned 
upon the three-wire system. Four different sizes of pipe, carry¬ 
ing correspondingly different sized conductors, are in common use, 
and are as follows : — 

1 h" pipe containing 80 M to 1*20 M circular mils of conductor. 

2" pipe containing 150 M to 300 M circular mils of conductor. 

2b" pipe containing 350 M to 000 M circular mils of conductor. 

3" pipe containing 700 M to one million circular mils of conductor. 

The cross-sections of the various sizes of electrical tube are 
shown in Fig. 123. To lay the mains, excavation is made in the 
street just under the surface of the pavement. Successive lengths 
of appropriate size electrical tubes are then laid loosely along the 
bottom of the trench ; each successive length is connected to its 
neighbor by means of a junction-box shown in Figs. 123 and 124. 

In the illustrations it will be seen that the two ends of the pipe 
enter an egg-shaped casting through two water-tight sleeves at 
either end of the oval. Inside of the casting, the separate con¬ 
ductors are joined by connectors formed of heavy copper rope. 
The connectors are screwed to the conductors by means of set 
screws running through copper castings on the ends of the con¬ 
necting rope. After the connectors are in place, they are thor¬ 
oughly soldered to the ends of the mains, thus making the electrical 
joint. The covering of the egg-shaped casting is screwed down 
upon the lower half; and by means of a small hole in the top of 
the casting, the whole of the box is filled full of melted insulating 
compound, thus forming an absolutely water-tight joint. To con¬ 
nect the consumer to the main line, a junction-box is provided 
which takes the place of the ordinary connecting-box joining the 
ends of the two successive pipe lengths, Fig. 124. The service-box 
is essentially the same as the junction-box, with the exception that it 
has three outlets instead of two, the third outlet forming a means 
whereby a third electrical tube may be carried from the street 


180 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


main to the inside of the wall of the premises of the consumer. 
At various points along the underground net-work, large distrib¬ 
uting-boxes are placed, into which all of the mains from several 



Fig. 123. Edison Tubes and Junction-Box. 


adjacent streets extend. By means of the flexible connections 
shown in bigs. 124 and 125, any desired combination or rearrange¬ 
ment of the circuits may be effected. The service-box also forms 
a ready means of testing and inspecting all of the circuits so as 
to insure their adequate and proper maintenance. The Edison 








THE CONSTRUCTION OF UNDERGROUND CIRCUIIS. 181 

system of conduit has in this country received very large develop¬ 
ment, a great proportion of our cities being supplied with incan¬ 
descent lights by means of this system. The Edison system presents 



Fig. 124. Edison Distributing and Seruice Boxes. 


the advantage that all the work of manufacture can be done in the 
factory by machinery, by skilled labor, and under the supervision 
of thoroughly competent inspectors. The street work simply con¬ 
sists in excavating an exceedingly shallow trench, and laying the 
mains loosely along the bottom of it, and in suitably connecting 












182 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


the ends of the adjacent tubes. While the Edison system is one 
of the most admirable that has been devised, it is obvious that it 
entails considerable expense on account of the necessity of providing 
each group of mains with a separate iron pipe. 

197. The Ferranti Mains. — A description of cable systems 
would not be complete without reference to the method success¬ 
fully put into practice in London by Mr. Farranti, involving trans¬ 
mission of alternating currents at a potential of 10,000 volts. 
Present practice would but rarely justify such pressures, but the 
time may not be far distant when this amount will be frequently 
exceeded. The Ferranti mains consist of two concentric copper 
tubes, A and E, Fig. 126, separated by half an inch of paper, C, 
saturated with black mineral wax, and protected from injury by a 
solid iron sheath, D. About thirty miles of these conductors have 



Fig. 125. Edison Distributing-Box. 


been made, and are working from the Deptford Station in London. 
The greater proportion of these conductors are designed to carry 
250 amperes, and consist of an inner tube -j 9 g" in diameter, giv¬ 
ing a cross-section of one-fourth of a square inch. This is separated 
from the outer tube by the requisite paper insulation, while in turn 
the outer tube is similarly separated from the iron sheath. A lon¬ 
gitudinal and cross-section of the main is indicated in Fig. 126. 

The chief point of interest lies in the construction of the joints 
in order that both the requisite insulation and conductivity should be 
secured. For convenience in handling, the mains are made in 20-ft. 
lengths; and the ends of each piece are turned to form long conical 
male and female sockets, as exhibited at A in the illustration. When 
the mains are laid, the successive lengths are forced into accurate 





THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 183 


contact by a hydraulic jack. The inner conductors are joined by a 
copper plug a , while the outer ones are connected by a copper sleeve 
G, that is secured by corrugating the sleeve onto the mains. 

198. Telegraph Cables. — For underground telegraph work, the 
cable is usually made by twisting together a sufficient number of 
carefully insulated wires to form the desired number of circuits. 
The wire chosen for the purpose is usually some one of the better 
forms of rubber-covered wire, to attain the requisite insulation. By 
means of twisting-machines, the conductors are laid up into a flex¬ 




ible rope, which is afterwards covered with one or more layers of 
heavy braid, treated with an insulating compound, in order to retain 
the circuits in their appropriate positions. Cables of this description 
may be made of any desired size, and supplied with circuits of either 
large or small wire, at the pleasure of the designer. For an addi¬ 
tional mechanical protection, they may be subsequently supplied with 
either a lead sheath or an armor of iron or steel wire. This, how¬ 
ever, is rarely necessary, excepting where specially severe service is 
to be expected. 

199. Subaqueous Cables. — Cases frequently arise where it is 
necessary to cross, with an electrical circuit, a stream or other body 
of water. Under these circumstances, a cable specially prepared 
is necessary, to resist the greater severity of the service. The cir¬ 
cuits may be arranged as already described for ordinary telegraph 


































































































184 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


cables, due care being observed to proportion the copper cross-sec¬ 
tion for the work which the cable is called upon to perform. After 
the circuits are laid up, it is necessary to afford the cable a much 
greater protection than is essential for ordinary underground lines. 
To this end subaqueous cables are frequently supplied with two or 
more sheaths, in order to make them absolutely waterproof, and then 
are supplied with an additional armor of iron or steel wire, which is 



Cop-pet Wire. 


Gutta Perch*, 
4 layers. 


Tarred Hemp. 


Iron Wires. 


Compound ot 
Asphalt 
and Sand. 



Strand of 
Copper Wire*. 


Gutta Perch*, 
3 layers. 


Tarred Hemp. 


Iron Wirer, 
* covered 
with Hemp. 


Fig. 127. Submarine Telegraph Cable. 


braided over the surface of the sheaths. For submarine telegraph 
work, the lead sheaths usually are omitted, as sufficient insulation 
can be obtained by covering the wire with a number of layers of 
insulating compound. The steel armor, however, is an absolute 
necessity, in order to protect the cable from injury during the 
period of laying, and to protect it from such destructive influences 
as chafing against rocks and other obstructions which may be found 
in the bed prepared for it, and to enable it to resist all injury which 
may be caused by the keels or anchors of passing vessels. In espe- 


























THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


185 


cially shallow water, extra precautions must be taken, as here the 
cable is much more liable to injury. Examples of submarine tele¬ 
graph cable construction are exemplified in Fig. 127. 

200. Power Circuits. — Cables for power circuits may be manu¬ 
factured of any desired capacity, and especially designed and adapted 
for particular cases of transmission. For copper cross-sections which 
are less than 100,000 circular mils, it is customary to use a solid 
conductor, which is overlaid with several layers of insulating material. 
For sizes larger than this, the stranded conductor becomes impera- 



Fig. 128. Power Cables. 


tive, as the solid rod is too stiff to permit of the necessary mechani¬ 
cal manipulations that are required for installation. The general 
appearance of such cables is indicated in Fig. 128. The practice of 
drawing a lead sheath over cables of all descriptions is rapidly in¬ 
creasing ; as it is found that the continuous film of lead affords an 
almost perfect protection to the cable, and guarantees to the insulat¬ 
ing material a much longer life than can be obtained in any other 
way. 

Experience has also shown that paper thoroughly impregnated 
with insulating compound, such as the various tars or resins, forms 

























186 


THE ELECTRICAL TRANSMISSION OE ENERGY. 






one of the best insulating materials, provided paper can be kept 
reasonably dry, as is insured by the use of the lead sheath. A very 
large class of distributing cables are now made with paper insulation, 
which give the highest satisfaction in actual service. Some of the 
varieties of paper insulated cables are shown in Fig. 129. 

201. The possible variety in design that could be attained for 
transmission cables is without limit. In Fig. 130, from Nos. 1 to 
22, a variety of cable cross-sections are shown which experience 
has indicated to be serviceable in various forms of transmission, 
and which may be obtained in the market without the necessity for 
special manufacture. 

No. 1, No. 3, and No. 15 are 
examples of feeder cable intended 
for three-wire distributing sys¬ 
tems. Nos. 1 and 3 contain 
stranded conductors. 

In No. 1 each con- 


Fig. 129. Paper Cables. 


ductor is surrounded by an independent lead sheath, while in 
No. 3 the lead sheath embraces all three of the mains. Nos. 1 
and 3 may be commonly obtained, having from 20,000 to 250,000 
circular mils. No. 15 contains no lead sheath, and solid con¬ 
ductors are used, as the cable is rarely called for excepting in small 
sizes. Nos. 2, 4, 6, 7, and 21 are examples of conductors with 
lead sheaths and exterior and interior insulation. They are stranded 
for the sake of greater flexibility, and may be obtained in all the 
commercial wire sizes. The finer strands, as in No. 2, No. 6, and 
No. i, are much more flexible than the coarse wire of No. 4. 
No. 5 is an unarmored, unsheathed submarine cable designed for 
































































Fig. 130. Sections of Transmission Cables. 


the construction of underground circuits. 187 


































188 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


transmission on the three-wire system. The two large conductors 
are intended for the outside mains, while the smaller one fills the 
office of the third wire. The three small conductors are intended 
to serve as pilot wires. Copper cross-section, 450,000 mils. Nos. 8, 
9, and 11 are feeder cables, designed for underground power distri¬ 
bution, and may be obtained up to 1,000,000 circular mils. No. 18 
is also a feeder cable, with an extra protection of the lead sheath. 
Nos. 20 and 22 are feeder cables with light insulation, but are only 
intended for interior work in dry locations, and not for underground 
service. Copper section up to 1,000,000 circular mils. Nos. 13 and 
19 are examples of solid lead-covered and plain insulated under¬ 
ground cable, suitable for arc-light service. Nos. 12 and 15 are 
similar triple-conductor cables of solid conductors. No. 16 is a triple¬ 
conductor concentric cable, with lead sheath, especially adapted to 
triphase transmission, or other high potential work. 

202. Telephone Cables. — For telephone service, cables are re¬ 
quired which possess slightly different characteristics from those 
which would meet the specifications for telegraphic or for power 
distribution. In the telephone service, it is found essential to reduce 
the electrostatic capacity to the lowest possible figure, in order to 
produce a conductor which shall have the requisite talking ability, 
and also to so arrange the conductors as to neutralize all the effects 
of either self-induction between the talking circuits, or induction 
produced by the presence of neighboring currents. To successfully 
accomplish these requisites, many experiments have been tried, pro¬ 
ducing a variety of cables that have been more or less successful. 

203. The British Post-Office Cable. — A cable largely in use 
by the English postal service is composed of tinned copper conduc¬ 
tors, each of three strands, aggregating a weight of about 20 lbs. 
per mile, with a resistance of 45 ohms per mile. Each conductor is 
covered with two coatings of india-rubber, and then taped with thin 
india-rubber coated cotton, and finally with ozokerite. The conduc¬ 
tors are then twisted together in pairs, and laid up in cables of the 
required number, served with jute, and wrapped with stout asphalted 
tape. After the core is thus completed, it receives an additional 
coating of hemp, and another layer of asphalted tape. 

204. The Patterson Cables. — The Patterson cables, made by 
the Western Electric Company, are composed of a number of copper 


THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


189 


conductors, usually of No. 18 or 19 gauge, which are insulated from 
each other by being loosely wrapped with a spiral layer of paper, and 
are then protected by means of a lead sheath. In the earlier cables 
it was thought necessary to secure the insulation by forcing liquefied 
paraffine into the cable, the paraffine being aerated with carbonic 
acid gas. By this means a very high insulation resistance was 
obtained, with a notable reduction in electrostatic capacity compared 
with the rubber cable. All cables of this description are made in 
twisted pairs ; the respective conductors, after being insulated, and 
before being laid up in the core, are twisted together to give a lay 
of one turn in some 5" to 7". The entire core is then formed by 
laying up successive pairs of twisted conductors* in a similar spiral 
manner. While the use of the aerated paraffine was found to be a 
marked improvement, so far as the electrostatic capacity was con¬ 
cerned, over the former methods, the cable was yet found to present 
an objectionable amount. To still further reduce this feature, re¬ 
course was had to the dry-core cable , which simply consists in paper- 
covered copper conductors laid up and covered with a lead sheath, 
with no other form of insulation. By this means a cable is obtained 
in which the dielectric consists largely of air. Cables of this descrip¬ 
tion are made as low as .06 microfarad per mile. The objection to 
this style of cable lies in its liability to injury, in case the lead sheath 
is ruptured, and the cable subjected to moisture. When the cables 
are manufactured, it is customary to seal each end of the cable by 
the introduction of paraffine or similar insulation, for a space of a 
few feet, in order to prevent the incursion of moisture when the 
cable shall be spliced. So long as the lead cover remains intact, no 
difficulty is experienced ; but a rupture of the lead is sufficient to 
admit moisture to the paper core, when by the capillary attraction of 
the paper, the moisture is liable to become distributed throughout 
the entire length of the cable, thus utterly ruining it. 

205. The W. T. Glover Cables. — The earlier cables manufac¬ 
tured by this firm were designed for grounded circuits, and were 
constructed in a manner to lessen and avoid cross-talk, and termed 
“Anti-Induction Cables.” The cable was formed of the requisite 
number of insulated wires, usually of No. 18 gauge. The wire was 
of tinned copper, insulated with several thicknesses of pure rubber 
strip, and served with prepared tape. A number of the wires in the 


190 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


cables were then coated with a continuous layer of tin-foil, and placed 
in definite positions in the cable, with regard to the remainder of the 
conductors. Inasmuch as the location of the wires covered with lead 
foil was accurately known, they served as a means of locating the 
positions of the other circuits. The arrangement of the wires in 
the cables also was such that the lead foils were all in electrical 
contact. The core thus formed was further protected by means of a 
lead sheath arranged to come in contact with the previously sheathed 
conductors. As a result, all of the sheaths were grounded by being 
connected to the exterior coating. This arrangement of sheathing 

• y 

was designed to intercept induced currents, and protect the cable 
from cross-talk and the other effects of induction. To design a 
cable for metallic circuits, a new form was arranged that has been 
termed the “ Magpie Cable.” This consists of a number of wires 
arranged in double pairs. The wires are insulated in the manner 
already described. The arrangement of the conductors is such that 
the wires are laid up in strands of four, one of each pair in each 
strand being covered with white tape and the other pair with black, 
thus serving as a means of distinguishment, in order that the ap¬ 
propriate conductors may be readily picked out and assigned in 
arranging the circuits. While these cables have found a wide 
introduction, the lead sheath and tin-foil wrapping cause them to 
have a very high electrostatic capacity, something like .27 of a 
microfarad per mile. 

206. The Fowler-Waring Cable. — Two different forms of 
cable are manufactured under this trade name. 

The first class, the Waring cable, is arranged by twisting to¬ 
gether a sufficient number of copper conductors and incasing them 
in a leaden sheath. When this is accomplished, the whole cable is 
forced full of heavy petroleum oil, something in the fashion of the 
Brooks system. It is claimed for this cable that it has the ability 
to resist very high temperatures without serious injury to the insula¬ 
tion. Experiments have been made which show that individual con¬ 
ductors may be heated nearly red-hot, or the exterior of the cable 
heated to the fusing-point of the leaden sheath, without serious 
injury. 

The second class of cables, known as the Dry Core, is made by 
wrapping the conductors with a specially prepared vegetable fiber, 


THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


191 


arranged to be non-hydroscopic. The wires are then twisted together 
and lead-covered. This arrangement attains practically the same re¬ 
sult as is secured by the paper cables, with the supposed advantage 
that the prepared fiber does not render the cable so likely to absorb 
moisture. The Waring cable has an electrostatic capacity of about 



Fig. 131. Sections of Felten-Guilleaume Cable. 


.16 of a microfarad, and the Dry Core about .07 of a microfarad 
per mile. 

207. The Felten-Guilleaume Cables. — The cables manufac¬ 
tured by this firm are similar, so far as their styles of rubber insula¬ 
tion are concerned, to those of other manufacturers ; but they offer 
a very ingenious and exceedingly valuable form of paper cable. The 



Fig. 132. A Twisted Pair. 


design of these cables is shown in the accompanying illustrations, 
Figs. 131 and 132, giving a cross-section and the method of making 
a single “twisted pair.” The conductors are arranged either in 
pairs or in fours, and are separated by a single strip or two strips 
of paper. From the illustration, it will be observed that each pair 
is made by laying between the copper conductors a strip of paper, 
which is then twisted, and subsequently surrounded with an addi- 








192 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


tional layer of paper. Each pair of conductors, or each set of four, 
is thus inclosed in a little paper tube separated transversely by one 
or two diaphragms of paper. After the completion of the core, the 
whole cable is incased in a leaden sheath, and then may be further 
protected by an additional layer of tape or of iron armor. I he paper 
for these cables is either ordinary dried paper, or it may be impreg¬ 
nated with an oil or resin to prevent the incursion of moisture. It 
is asserted that specimens of these cables have been shown with a 
capacity as low as .05 microfarad per mile. The same firm also 
manufactures at present the most successful telephone cables for 
submarine work. The same system is used, but the construction 
for marine work is necessarily somewhat different. 

A marine cable containing four conductors is shown in Fig. 133. 



133. The Guilleaume Submarine Telephone Cable. 


The four conductors, with their cross-shaped paper diaphragm, are 
seen at the center of the cross-section. The group is then wrapped 
with paper, as previously indicated. This is then sheathed in a lead 
tube, which is afterwards supplied with an additional insulation in 
the shape of a double coating of gutta-percha. The armor of the 
cable, instead of being ordinary iron wire, is formed of galvanized 
wires so arranged that they lock into each other, forming an envel¬ 
ope that is exceedingly firm and incompressible, and which effectu¬ 
ally protects the paper of the cable core from becoming compressed, 
and the conductor short-circuited. 

208. The Herrmann Beaded Cable. — One of the early attempts 
looking toward the reduction of electrostatic capacity for telephone 
cables was an invention by Herrmann, who conceived the idea of 
incasing the several conductors of cables in a series of wooden beads, 



















THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


193 


and then sliding them inside of the common leaden sheath. This 
construction is indicated in Fig:. 134. 

W hile this invention did secure a considerable reduction in the 
capacity over ordinary rubber insulators, it is more expensive, and 
has a still greater capacity than the present form of paper cables. 

209. Cable Joints and Splices. — The operation of joining 
underground conductors having a solid core consisting of a single 
strand, or splicing multi-circuit cables, is one which requires the 
exercise of extreme care and the employment of the very best skill 
and workmanship, in order to make splices which shall be durable 
and lasting, and which shall continuously preserve the conductors 
from the incursion of moisture. 




Case 1. Single-Conductor Cables. — For splices or branches in 
single-conductor cables, the work should be performed as in Fig. 
135, Nos. 1 to 14 inclusive. In order to splice a single stranded 
cable, the insulation should be carefully laid bare for a length of from 
3" to 6", depending upon the size of the cable core. At either 
end the insulation should be carefully tapered away to form a long 
cone. The strands of the cable should next be tightly twisted 
together and dipped in solder, to secure the ends of individual wires. 
The ends may then be beveled, as indicated in No. 6, with a long 
scarf, which should then be thoroughly and carefully soldered to¬ 
gether, under no circumstances using any acid as a solder flux. 
When the scarf is thoroughly soldered, it should then be wrappc.l 
with a continuous tight serving of copper wire, as indicated in No. 2. 
The joint is then completed, as shown in Nos. 3, 4, and 5, by wrap- 




























194 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


ping layer after layer of okonite tape around the joint, until a 
smooth, conical splice is obtained, as indicated in No. 5. 

Solid conductors may be spliced in a similar manner, as indicated 
in Nos. 6, 7, and 8. A branch in a cable may be taken off in a 

manner similar to that in¬ 
dicated for splicing, ex¬ 
cepting in so far as the 
description of that pro¬ 
cess refers to the actual 
joining of the conductors 
in the cable. The process 
for taking off a branch is 
indicated in Nos. 11 to 14 
inclusive. Here the insu¬ 
lation of the cable is laid 
bare for a couple of inches, 
the insulation being care¬ 
fully tapered away on each 
side. The branch is then 
firmly lashed to the cable 
by means of a serving of 
copper wire, as indicated 
in No. 2, the whole being 
securely and firmly sol¬ 
dered to the cable core. 
The insulation is then re¬ 
placed in a manner simi¬ 
lar to that for making 
splices, excepting that the 
layers of tape must be 

served over the branch as 
hg. 135. Cable Splices. We ll as Over the C01*e of 

the cable itself, the final completed joint being finished as shown in 
No. 14. 

210. Case 2. Multi-Conductor Cables. — For all of the special 
forms of cables, such as those made by the Siemens Bros, and 
the Edison Company, special methods of splicing are used, which 
have been indicated in the accounts of the respective styles of cables. 












































































































































































THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 


195 


For multi-conductor cables of rubber insulation, a length of the 
cable from 8' to 2 ft. in length, depending upon the number of cir¬ 
cuits, must be laid bare of insulation. The separate circuits must 
then be carefully untwisted from each other, each circuit being 
properly tagged to preserve its identity. The insulation must 
then be removed from each of the individual wires. The splice is 
effected by twisting together and soldering each conductor to the 
conductor to which it is assigned in the new piece of cable. Insula¬ 
tion, usually consisting of okonite tape, or some equivalent rubber 

compound, is then replaced upon each of the individual circuits, the 
circuit replaced in as compact a form as possible, and the whole 
splice completed by three or four layers of okonite tape serving the 
entire cable and binding the circuits into position. With special 

skill, splices may thus be made in okonite cable, which can hardly 

be detected from the regular cable. 

Lead-covered cables with paper compound cores may be spliced 
by cutting away the lead sheath, exposing the conductors, and spli¬ 
cing them, as has already been indicated. As soon as the splice is 
completed, a piece of lead pipe of sufficient size, previously slipped 
over the cable, may be soldered to the lead sheath on either side of 
the splice, making an absolutely water-tight joint. 

For dry-core paper cables, an additional process is necessary to 
seal either end of the cable to prevent the entrance of moisture 
while the splice is being made. To this end, as soon as the cable is 
opened, it is thoroughly heated and dried by immersing it in a bath 
of boiling paraffine oil, and then hot paraffine is poured into the 
cable to entirely fill it up, and seal it for the space of some 2 or 
3 ft. This is done on each end of the pieces to be spliced ; and 
then the conductors are connected, and are insulated by being cov¬ 
ered with paper tubes, the whole core bound together with tape, 
and a lead sleeve soldered over the joint. With careful workman¬ 
ship, splices of this kind can be made without injuring the cable in 
any respect, and without increasing its diameter at the splice more 
than fifty per cent over that of the original cable. 

211. The Connection of Underground and Aerial Systems. — 
The connection of underground and aerial systems is a problem of 
great practical importance. It is customary to construct at the junc¬ 
tion between the pole-line and the conduit system, a vault or man- 


196 


THE ELECTRICAL TRANSMISSION OF ENERGY. 



hole of the requisite dimensions, directly at the base of the anchor 

pole forming the end 
of the pole-line. From 
this vault, iron pipes 
of sufficient diameter 
to permit easy intro¬ 
duction of the neces¬ 
sary cables are run up 
alongside of the poles 
to such a distance 
above the street as to 
secure the cable from 
malicious injury. The 
pipes extend through 
the earth, and are built 
through the wall of the 
vault, with a curve of 
some 5 or 6 ft. radius, 
to permit of the easy 
introduction of the ca¬ 
ble. The necessary 
cables are then passed 
through the iron pipes, 
up the side of the pole, 
and are terminated in 
cable heads, usually 
placed upon a balcony 
or platform, set di¬ 
rectly under the lowest 
cross-arm, Fig. 136. 

The cable head is 
a rectangular cast-iron 
box, represented in 
Fig. 137, about 4" in 
thickness, some 8" or 

Fig. 136. Cable Terminal Pole. 9 ” widtll > alld Var >'- 

ing from 18" to 4 ft. 

i:i length, in order to accommodate from twenty-five to one hun- 




















THE CONSTRUCTION OF UNDERGROUND CIRCUITS. 197 



dred pairs of wires. The lower extremity of the box terminates in 
a brass tube, which, being threaded into the casting, forms a water¬ 
tight joint. 1 he sleeve of the cable is 
soldered to the brass thimble, thus com¬ 
pleting the connection between the box 
and cable. The office of the cable-box 
is to afford a water-tight compartment 
having a sufficient number of binding- 
posts to correspond to the number of 
wires in the cable. Upon the comple¬ 
tion of the soldering of the cable sheath 
to the brass thimble at the base of the 
box, the wires composing the cable are 
untwisted inside of the cable-box, and 
each one soldered to the interior termi¬ 
nal of the binding-post. By this means 
the wires from the cables are extended 
through the cable-box to the exterior, in 
such a manner as to make a waterproof 
connection, and to afford an easy and 
rapid means of distribution to the pole¬ 
line. The appropriate number of cable- 
heads, corresponding to the number of 
cables ending in any pole-line, are placed 
in a circular wooden compartment built 
around the pole above the top of the bal¬ 
cony. The entire construction is indi¬ 
cated in Fig. 136, showing the balcony, 
cable-box, and cables to the aerial line. 

The sides of the cable-head, as repre¬ 
sented in Fig. 137, are supplied with 
lightning arresters, of the pattern shown 
in Fig. 89. As aerial lines are particu¬ 
larly subject to the incursion of strong 
currents, these protectors are a neces¬ 
sity, to guard the cable wires from in¬ 
jury that would be much more serious than any damage resulting to 
the pole conductors. 






















198 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


CHAPTER V. 

ELECTRICAL INSTRUMENTS. 

Art. 212. No exposition of the methods of distributing electrical 
energy would be complete without such reference to the various 
electrical instruments, and methods of measurement, as will enable 
the designer to accurately inspect the condition, and determine the 
performance, of electrical circuits. The principal electrical instru¬ 
ments may be divided into five classes : — 

First. Instruments for the measurement of resistance. 

Second. Instruments for the measurement of the quantity of 
electricity. 

Third. Instruments for measuring electrical pressure. 

Fourth. Instruments for the measurement of capacity. 

Fifth. Instruments for the measurement of the energy delivered 
by a circuit. 


INSTRUMENTS FOR THE MEASUREMENT OF RESISTANCE. 


213. The Wheatstone Bridge. — The most widely known instru¬ 
ment for resistance determinations is the Wheatstone Bridge, the 
theoretical arrangement being shown in Fig. 138. Four resistances, 
a , b, d, and x, are arranged in the form of a parallelogram, a battery 
being placed in series with one diagonal and a galvanometer in the 
other. When the four resistances forming the sides of the bridge 
are so adjusted that no current flows through the galvanometer, these 
resistances bear a certain definite relation each to the other. When 
there is no current between the points A and C, the galvanometer 
may be removed without altering the current in the arms of the 
bridge. Also, the points A and C may be short-circuited without 
interfering with the balance. Suppose the points A and C to be 
separated ; then the joint resistance of the four arms of the bridge 

(a -f- x) (b d) 


between the points B and E will be, 


a -f- x b -f d ' 


If now the 




ELECTRICAL INSTRUMENTS. 


199 


points A and C be joined, the resistance may be expressed as 
ab dx 

a ^ ^ . These two expressions are evidently equal to each 

other, and may be stated in the form of an equation,— 


(a 4~ x ) (b -f- d) _ ab . dx 
ci -{- x -f- b d ci —|- b d — j- x 

which, by simplification, may be reduced to the form 

ad 

x — —. 
b 



(23) 


Therefore, if three of the quantities of this equation are known, the 
fourth can be easily determined. Usually two of the arms consist of 
fixed known resistances, the third is an adjustable resistance formed 
of a number of coils whose value has been previously determined, 
while the fourth is the 

c 

unknown resistance 
which it is desired to 
measure. By the sim¬ 
plest method, a and 
b would be of equal 
value, in which case 
would be equal to d ; 
or, in other words, the 
resistance between A 
and E, when the equi¬ 
librium is obtained, 
gives the value of the 
resistance to be measured. It is essential that some resistance should 
be in the arms a and b ; for otherwise the galvanometer is short-cir¬ 
cuited, and equilibrium will always be apparently produced. Instead 
of using equal resistances in a and b, one of the two may be 10, 100, 
or 1000 times as great as the other ; or, in fact, any multiple that may 
be desired. Multiples of ten, however, are those which are most com¬ 
monly used. If b is made ten times as large as a, the resistance in 
d will be ten times as large as x, and thus every unit of resistance in d 
will represent one-tenth of a unit in x. By this means it is practical to 
determine the value of the unknown resistance to the tenth of a unit. 
Similarly, by making d 100 or 1000 times as large as a } the value of 



















200 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


x may be correspondingly ascertained to the T ^o or toVo of a unit. 
If, on the contrary, a be made 10, 100, or 1000 times as large as b, 
each unit in d must be multiplied by the corresponding factor of 10, 
100, or 1000, to give the value of x. By this means it is practical 
to make the bridge measure very small or very large resistances, 
with fair accuracy. It is obvious that the sensitiveness of the gal¬ 
vanometer employed to detect the current flowing between A and C 



Fig 139. Portable Testing Set 


forms a large factor in the accuracy of bridge measurements. The 
more sensitive the galvanometer, the smaller the current it will be 
possible to detect, and the nearer the bridge arms can be brought to 
an exact balance. A very convenient and portable form of testing- 
set, embracing resistance coils, bridge, and galvanometer bridge, is 
shown in Fig. 189. 

At the extreme right of the cut is shown a small D’Arsonval gal¬ 
vanometer, having the advantage of being dead-beat. Next to the 
galvanometer is the resistance-box, containing four sets of coils, 
units, tens, hundreds, and thousands ; and on the extreme left hand, 



































































































































































































































ELECTRICAL INSTRUMENTS. 


201 


the arms of the bridge, a and b are seen, the arm a having coils of 
1, 10, and 100 ohms, and arm b with coils of 10, 100, and 1000 
ohms. By means of pegs, the arms can be arranged either to multi¬ 
ply or divide at pleasure. With the coils in the arms a and b, ratios 
of 1 to 10, 100, or 1000 can be obtained, either multiplying or divid¬ 
ing; and as the resistance coils measure from 1 ohm to 1111 ohms, 
the set can measure from Woo of an ohm to 11 megohms. 

214. The Slide Wire Bridge. — While the previously described 
form of bridge is capable of detecting a thousandth of an ohm, very 
low resistances are more conveniently measured by a modification of 
this instrument, termed a “slide wire bridge,” as shown in Fig. 140. 



The illustration indicates the simplest and cheapest form of the 
apparatus, consisting of a baseboard of insulating material upon 
which are placed three heavy copper bands, A, B, and C. Between 
the bands A and B, and B and C, are gaps into which any desired 
resistance coils may be placed. The other ends of the pieces A and 
C are joined by a uniform wire, having a resistance proportioned to 
the capacity of the measurement that it is desired to make. Parallel 
to this wire a scale is placed, having its initial and final points ex¬ 
actly opposite the places where the measuring-wire is connected to 
the heavy copper bars. 

The scale should be graduated to read both ways ; and on the 
assumption that the wire is of uniform resistance throughout, and 
also that the scale properly corresponds to the beginning and end of 
the wire, the ratios of the resistances r and r' may be read from the 
two segments into which any point, such as “B',” divides the wire 
















202 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


and the scale. The point B' forms a sliding contact on the wire, 
extending from the middle of the bar B to the wire, and including 
the galvanometer in its circuit. 

By examination of the illustration, it will be easy to trace the 
similarity of the circuits to those of the ordinary Wheatstone bridge. 
Thus it is evident that the “slide wire bridge” is merely such a 
modification of the ordinary Wheatstone arrangement as will permit 
the introduction of any desired low resistances at the points r' and 
r, and the use of a uniform wire for the variable resistance arm, in 
order that the variable resistance may be obtained in sufficiently 
small fractions of a unit. 

215. The Ohm-Meter. — It is an obvious consequence from 
Ohm’s law that the resistance of any circuit, or portion of a circuit, 
may be calculated by measuring the electro-motive force operating, 
and the amount of current flowing. It is not uncommon to measure 
the insulation of heavy circuits by ascertaining the difference of po¬ 
tential at the terminals of the dynamo supplying circuit, and then, by 
means of a milliammeter, determining the leakage between the circuit 
and the ground, the quotient of these quantities being the desired 
resistance. The objection to this method is that it requires a simul¬ 
taneous reading of two instruments, which, in cases of varying 
currents and varying potentials, is difficult to obtain. As an im¬ 
provement, an instrument termed the ohm-meter has been devised, 
that consists of two circuits, one of fine wire and another of coarse 
wire. At the intersection of the two coils a magnetized needle is 
suspended, carrying a pointer, that, playing over a scale, serves to 
determine the readings of the instrument. Using the apparatus, the 
fine wire coil is connected across the terminals of the circuit, serving, 
by its effect upon the magnetized needle, to determine the electric 
pressure ; while the coarse wire is connected in series with the cir¬ 
cuit whose resistance is desired, and affects the needle proportionally 
to the amount of current flowing. By the combined action of the 
two coils, the needle assumes a position of equilibrium, which is in 
proportion to the resistance of the circuit. An instrument of this 
description forms an exceedingly useful auxiliary for all circuits car¬ 
rying heavy currents, as by means of its aid the insulation or resist¬ 
ance of the circuit may be continually determined, even during the 
time that the plant is under full operation. 


ELEC ERICA L INS 7 R UMENTS. 


203 


216. Another form of ohm-meter, very useful for measuring low 
resistances, may be constructed by arranging a differential galva¬ 
nometer so that the coils of the instrument may be moved either 
toward or away from the needle, by means of a micrometer screw, 
so arranged that the position of each coil may be accurately deter¬ 
mined. 

To measure a resistance, a known resistance is placed in one half 
of the differential galvanometer circuit, and the unknown in the 
other half. The coils are then adjusted until no deflection is pro¬ 
duced on the needle. The relative positions, then, of the two coils, 
give accurate indications of the unknown resistance in terms of the 
known resistance. With a sensitive reflecting galvanometer arranged 
in this manner, it is perfectly practicable to measure one-millionth of 
an ohm with accuracy. 

INSTRUMENTS FOR MEASURING ELECTRICAL QUANTITY AND 

PRESSURE. 

217. Galvanometer. — Nearly all practical instruments for esti¬ 
mating either current or electro-motive force are based on the 
mutual reactions developed either between a coil of wire and a mag¬ 
netic field, or between two coils of wire, when arranged to form a 
part of the circuit it is desired to measure, the only notable excep¬ 
tion being in the case of the hot wire and electrostatic voltmeters, to 
which special reference will be made. Galvanometers, as these elec¬ 
tro-magnetic instruments are broadly termed, may be used in three 
distinct ways : — 

First. Simply to detect the presence of a current. 

Second. When constructed so that their indications are propor¬ 
tional to the electro-motive force, they become volt¬ 
meters or pressure indicators. 

Third. When the readings correspond to the quantity of current 
they are termed ammeters. 

As a current indicator, the Thomson Reflecting Galvanometer 
is too well known to need more than passing reference. It is the 
instrument universally employed for all accurate work involving cur¬ 
rents of small magnitude, such as insulation, resistance, and capacity 
tests. The present forms of this instrument are made to permit the 
use of a number of interchangeable coils ; so, by proper calibration, 


204 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


the galvanometer may serve either as a voltmeter or an ammeter. 
As the Thomson instrument is very sensitive to the slightest varia¬ 
tion in the external magnetic field, and as it is not dead-beat, its use 
is almost restricted to laboratory work, and the most refined methods 
of testing. 



Fig. 141. The D'Arsonual Galvanometer. 


218. The D’Arsonval Galvanometer. — In the D’Arsonval Gal¬ 
vanometer, Fig. 141, an instrument is obtained, which, while it lacks 
the extreme sensitiveness and delicacy of the Thomson, is better 
adapted to the general practice of the electrical engineer. In this 
instrument the magnetic system is fixed, the poles of which are 
hollow and inclose a suspended coil of very fine wire, through which 





































































ELECTRICAL INSTRUMENTS. 


205 


the current to be measured circulates. By this arrangement the 
instrument is rendered independent of any surrounding magnetic 
fields, and can be used in close proximity to the largest dynamos ; 
and when used with a short-circuiting key, is perfectly dead-beat. 
Supplied with a reflecting mirror, reading telescope, and scale, suffi¬ 
cient accuracy and sensitiveness may be obtained for everything but 
the most delicate tests. 

219. The Ballistic Galvanometer. — For some measurements, 
notably in capacity testing, it is essential to employ a certain modi¬ 
fication of the above instruments, usually termed a ballistic galvanom¬ 
eter. The object of this device is to enable accurate determinations 
of transient currents, such as are produced by the discharge of a 
condenser, or currents developed by electro-magnetic induction. In 
the ballistic galvanometer the needle system is so arranged that 
movement does not (practically) take place until the transient cur¬ 
rent has ceased. Thus, as its name indicates, the instrument is 
intended to measure impulses. It is now customary to supply the 
best Thomson and D’Arsonval instruments with interchangeable 
needle systems for the purpose of ballistic work. The ballistic 
needle is usually a thimble or bell-shaped magnet, arranged that its 
rotation may be as little retarded as possible. The relation between 
an electric discharge and its effect on a ballistic galvanometer is 
given by the following formula : — 

Let Q = the quantity of electricity in coulombs. 

T = the time in seconds required for one complete oscillation. 

D = deflection with Q coulombs. 

F = figure of merit with a constant current. 

Then it can be shown that — 



(25) 


For example. Suppose the discharge from a certain condenser 
gives a throw of 120 divisions on the scale of a ballistic galvanom¬ 
eter, the figure of merit of which is .0002082 amperes, and time of 
oscillation 6 seconds ; what was the amount of electricity ? Here 


T = Q> 

D = 120 
F = .0002082 


G X 120 X .00020082 
2 X 3.14159 


= .0239 coulombs. 





206 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


For the full demonstration of this formula, the reader is referred to 
any of the extended works on testing, particularly that of Kempe. 

220. The constant of a galvanometer may be defined as the 
relation existing between the deflection indicated on the scale, the 
current, and resistance of the circuit. 

For example. Suppose a galvanometer having a resistance of 
r= 10,000 ohms is connected with a battery having an internal re¬ 
sistance r' = 200 ohms, and an external resistance r" =100,000 ohms, 
giving: a deflection of 20 divisions. The total resistance of the cir- 
cuit is 110,200 ohms; therefore, as the current in the circuit is 
inversely proportional to the total resistance, and as the deflection 
is assumed to be directly proportioned to the current, the constant 
would be 110,200 x 20 = 2,204,000. As any change in the resistance 
of the circuit will change the deflection, it is possible to use the con¬ 
stant to determine unknown resistance. Indeed, this is the most 
common method used to measure high resistances, such as the insu¬ 
lation of circuits. 

221. The figure of merit of a galvanometer is the amount of 
current which will produce a deflection of one division or one degree 
upon the scale. To find this current, it is only necessary to connect 
up the galvanometer and battery, in series, with a known resistance, 
and then to measure the deflection produced. Having the total 
resistance, it becomes a simple matter to calculate the amount of 
current flowing, and from this to deduce the quantity of current 
necessary to produce a deflection of one division, which, by defini¬ 
tion, is the figure of merit. 

For example. Suppose a galvanometer having a resistance of 
1,000 ohms to give a deflection of 100 divisions when joined with a 
battery of 250 ohms and an external resistance of 10,000 ohms, the 
battery having an electro-motive force of 100 volts. As the total 
resistance of the circuit is 11,250 ohms, the electro-motive force of 
100 volts will produce a current of .0089 of an ampere. Under 
these circumstances, as the deflection is 100 divisions, the figure of 
merit of the galvanometer will be .0089 divided by 100 = .000089 
of an ampere. That is, .000089 of an ampere will produce a de¬ 
flection of one division. 

222. A galvanometer having a high figure of merit is one the 
needle of which will deflect from zero with a very small amount of 


ELECTRICAL INSTRUMENTS. 


207 


I 


current. This, however, does not necessarily convey the idea of sen¬ 
sitiveness, for by a sensitive galvanometer is meant one whose needle 
when deflected under the influence of a current will change perceptibly 
with very small variation in the current itself. To attain a truly 
sensitive instrument, it is essential that the needle system should 
have a fiber suspension, as it is impossible to obtain sensitiveness 
with any other means. 

223. Reduction to Zero. — The angular deviation of a needle 
system in reflecting galvanometers is so small that it is usually cus¬ 
tomary to assume that the number of divisions in the deflection is 
proportional to the current that produced it.* While for instruments 
of this class this assumption is essentially true, it is not mathemati¬ 
cally correct. For precise work, therefore, it is desirable, as far as 
possible, to use methods involving “ reduction zero ; ” as in this case 
the final balance obtained is with a zero reading, which must neces¬ 
sarily be precisely accurate. 

224. Inferred Zero. — In a reflecting galvanometer, the angle 
of maximum sensitiveness is the largest deflection that can practi¬ 
cally be obtained ; as, however, under any circumstances, the deflec¬ 
tion is only a few degrees, the true maximum angle of sensitiveness 
can rarely, if ever, be reached. The method of inferred zero here 
comes into play, by means of which increased sensitiveness can 
readily be obtained. By moving the controlling magnet so that the 
needle is turned away from the scale to a considerable distance, the 
readable deflection of the galvanometer can be largely increased. 

For example. Suppose the needle normally on the zero of the 
scale, and that a given current causes it to deflect through 300 di¬ 
visions. Then an increase in the current of one per cent would 
increase the deflection 300x101/100 = 303, an increase of three 
divisions. Suppose now that the working zero be placed 400 divis¬ 
ions away from the scale zero, and that the current has been suffi¬ 
ciently strong to produce a deflection of 300 divisions on the scale, 
the actual deflection would therefore be equal to 400 + 300 = 700, 
and an increase in the current of one per cent would increase the 
deflection to 700x101/100 = 707, or a deflection of seven additional 
divisions, for the same small increase of current. It will thus be 
apparent that the sensitiveness of the instrument may in this man¬ 
ner be very largely increased. An additional use of the inferred 




208 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


zero is to be found in making insulation or capacity measurements, 
when the standard, by means of which the galvanometer constant 
is determined, produces a current through the instrument which is 
widely different from the current used in making the test. 

225. Galvanometer Shunts. — The deflection of a galvanometer 
being proportional to the current traversing its coils, and the scale 
being of limited extent, it frequently happens that the current under 
examination is sufficient to carry the index off the scale, giving a 
deflection that is unreadable. It is usual, in such cases, to place in 

parallel between the terminals of the gal¬ 
vanometer an amount of resistance suf¬ 
ficient to permit of a readable deflection. 
Such a resistance placed in parallel with 
the galvanometer is called a “ Shunt.” 
In Fig. 142, let G be the resistance of 

Fig. 142. Diagram of Shunt Connection. . . „ . - . . 

the galvanometer, S that ot the shunt, 
/ the total current, and i and i' the currents in the galvanometer 
coils and shunt respectively, then — 



/=/+ f'- (26) 

As the electro-motive force is the same in both branches, the 
respective currents will be inversely as the resistance of each branch ; 
hence 

j = (f (27), and «' = *• X ; (28) 

» 

replacing i' by its value found from equation (27), 


I — i X 


G+ S 
S 


(29) 


Knowing the deflection given by the galvanometer with a known 
current, the current i is determined ; and from the known resistance 
G and S, I is readily calculated. The deflection that would be pro¬ 
duced on the scale with the current /, assuming the law of propor¬ 
tional deflection to hold true indefinitely, is evidently the deflection 

given by i multiplied by the factor--—. This factor is termed 


the multiplying 
m. Thus — 


power of the shunt, and is frequently symbolized by 


g + S 
s 


m. 










RLE C TRICA L INS TR UAIR NTS. 


209 


Suppose a galvanometer of 6340 ohms, when shunted with 10 
ohms, to give a deflection of 125 divisions, then — 


125 X 


6340 + 10 
10 


125 X 635 = 79375 divisions. 


In this case m = 635. Any known resistance may be used as a 
shunt, though for rapid work easy multipliers should be selected. 


As, — 


m = 


_ G -j- -S’ /< 


S’ 


(31), 


S = 


m — 1 


(32) 



Fig. 143. *The Weston Voltmeter. 


an expression giving the amount of resistance to be placed in a shunt 
to give any desired multiplying power in. The best galvanometers 
are accompanied by shunt-boxes having multiples of 10, 100, and 
1000. 

226. The Weston Instruments. — For the field-work of electri¬ 
cal engineers, the series of instruments manufactured by the Weston 
Electrical Instrument Co. are eminently desirable. The general form 
of the Weston instrument is shown in Fig. 143, from which it will 

























































> 


210 THE ELECTRICAL TRANSMISSION OF ENERGY. 

' appear that the instrument consists of a small, square mahogany box, 
about 6" on each side, and about 1" in thickness, which carries a raised 
brass framework, under which may be seen a graduated scale, over 
which a pointer travels. The mechanism of the instrument is shown 
in Fig. 144, and consists of a powerful horseshoe magnet carrying 
two enlarged pole pieces. Between the polar extensions a fine wire 
coil is delicately pivoted upon jewel bearings. To this movable coil is 
attached the pointer, or index, which plays over a graduated scale. If 
a coil of wire carrying an electrical current is placed between the 
poles of a magnet, it will tend to set itself at right angles to the lines 



Fig. 144. Needle-Bearing Weston Instrument. 


of force. In order to make a measuring-instrument, it is necessary 
that this tendency to turn be opposed by some well-known graduated 
counter-force. In the Weston instrument this is accomplished by 
introducing two flat spiral springs, fastened to the ends of the coil 
above and below, close to the bearings. When no current is in the 
instrument, these springs will keep the coil at a certain zero position, 
from which it will be deflected in proportion to the current through 
the coil. The pointer may therefore be arranged to move over an 
appropriately graduated scale, giving indications, which, by proper 
calibration, will be of great precision. Long experience and great 
care in workmanship have served to refine the details of the Weston 
instruments until they are exceedingly reliable. They are now made 































































































































ELECTRICAL INSTRUMENTS. 


211 


to cover every practical range of capacity, and are designed to be 
used either as ammeters, voltmeters, or wattmeters. They are 
further arranged to be used either on direct or alternating currents. 

As the Weston instruments are perfectly dead-beat, and will give 
fairly reliable readings in even so unfavorable a location as a jolting 
electric car, they form an essential part of the electrician’s outfit. 
For work requiring particular accuracy, the instruments should be 
recently calibrated, set quite level, carefully oriented, removed from 
powerfully varying magnetic fields, and corrected for temperature. 

The instruments thus far described have all been of the gal¬ 
vanometer type, and are open to the objections of requiring frequent 
calibration ; of sensitiveness to surrounding magnetic fields ; of intro¬ 
ducing a slight error by consuming in themselves a small fraction of 
the energy of the circuit to which they are applied ; and of requiring 



temperature corrections when accurate work is desired. To obviate 
these difficulties many devices have been proposed, among the most 
successful of which the Cardew voltmeter and the electrostatic volt¬ 
meters of Lord Kelvin may be mentioned. 

227. The Cardew Voltmeter. — The operation of the Cardew 
instrument depends upon the expansion produced in a long fine wire, 
due to the amount of heat developed in the wire by the current flow¬ 
ing through it. The heating effect of a circuit is proportional to the 
square of the current, and to the resistance of the circuit. By mak¬ 
ing the resistance extremely high, the amount of current becomes 
proportional to the electric pressure. In the Cardew voltmeter a 
long fine wire gives the necessary resistance. The instrument is 
shown in Fig. 145, and a view of the mechanism in Fig. 146. 

The wire is stretched under the action of a spring, and by suit¬ 
able mechanism is connected with a registering pointer. When 
applied to a circuit, a small fraction of the current passes through the 









212 


> 


THE ELECTRICAL TRANSMISSION OF ENERGY. 



Fig. 146. The Mechanism of the Cardew Voltmeter. 



Fig. 147. The Electrostatic Voltmeter. 

























































































































































































































































































































































































































ELECTRICAL INSTRUMENTS. 


213 


line wire, and, being transformed into heat, expands it. The move¬ 
ment of the needle really records the amount of this expansion, 
which by proper calibration may be made to read in terms of the 
voltage of the circuit. This instrument is perfectly dead-beat; abso¬ 
lutely insensitive to all magnetic fields ; and, when carefully made, 
forms within a limited range an instrument of great precision. 

228. The Electrostatic Voltmeter. — The Kelvin voltmeters 
are constructed on the principle of an air condenser, one of the sets 
of plates of which is movable about an axis in such a manner that 
the capacity of the apparatus may be either increased or diminished. 
The instruments are so designed that, under the influence of an 
electrostatic stress, the pointers indicate the tension produced. They 
cover the widest range, having capacities to measure from 40 to 
100,000 volts. As they take no current, they are insensitive to 
changes in temperature and to varying magnetic fields, and intro¬ 
duce no errors into the circuits to which they are applied. One form 
of the instrument is shown in Fig. 147. 

The instrument consists of quadrant-shaped plates inclosed in a 
glass case with metal back, the plates being in metallic connection, 
and nearly surround an aluminum plate suspended between them. 
The movable aluminum plate carries a pointer which indicates on a 
scale at the top of the case the difference of potential between the 
two parts of the condenser. When the fixed and movable plates are 
connected to two points of an electric circuit, between which there 
exists a difference of potential, the movable plate places itself in 
such a position as to augment the capacity of the instrument, and the 
magnitude of the displacing force is proportional to the square of 
the difference of potential acting upon the plates. This force is 
counterbalanced by means of a weight which can be hung upon a 
knife-edge at the lower extremity of the movable plate. In order to 
economize time in making readings, there is a device for checking the 
oscillations of the movable plate, and stops are introduced to limit 
its range of motion, and prevent damage to the indicator. The scale 
of the instrument is graduated from 0 to 60, the divisions indicating 
equal differences of potential. The actual value of any division 
depends upon the weight that is placed upon the knife-edge of the 
movable plate. With each instrument a set of three weights is 
usually supplied, having ratios of 1, 2, and 4. When the smallest 


214 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


weight is used, each division indicates 50 volts ; with the second, 
100 ; and with the third, 200 volts. 

229. Siemens Dynamometer. — This instrument consists of 
two coils of wire, one fixed and one movable, which are arranged as 
in Fig. 148, so the movable coil surrounds the fixed coil placed in 
the center of the instrument. By the means of binding-posts on the 
base, the current to be measured may be caused to flow through 
both the fixed and the movable coil. The movable coil is sus¬ 
pended from the top of the instrument by means of a spiral spring 

attached to a knob which carries a 
pointer playing over a graduated scale. 
When a current is passed through the 
instrument, there is mutual attraction set 
up between the movable coil and the 
fixed coil. The movable coil, therefore,, 
swings about its axis, and, by means of 
the spiral spring and milled head, may 
be brought back to its original position 
at right angles to the fixed coil. The 
number of degrees or divisions of the 
scale through which it is necessary to 
turn the head forms a measure of the 
current. It is usual to accompany these 
instruments with a tabular statement 
showing the value of the divisions on 
the scale. When wound with coarse 
wire, this instrument may be used for 
measuring current strengths of any de¬ 
sired amount up to several thousand amperes. When wound with 
fine wire, a similar instrument may be used as a voltmeter; and by 
winding the fixed coil with coarse wire, and the movable coil with 
fine wire, the instrument becomes a wattmeter whose indications are 
proportional to the total energy flowing through the circuit. 

230. Condensers. — When one conductor is adjacent to another 
it possesses the property of storing upon its surface a quantity of 
electrical energy. This quality is called the capacity of the conduc¬ 
tor, and plays an important part in the development of electrical 
circuits. The capacity of a conductor may be numerically defined as 



Fig. 148. Siemens Dynamometer. 























































































ELECTR1CA L INSTR UMENTS. 


215 


the number of coulombs of electricity required to be given to the 
one conductor in order to produce a difference of potential of one 
volt between it and the other. The capacity of a conductor depends 
upon its geometrical shape, upon its position relatively to the neigh¬ 
boring conductor, and on the characteristics of the dielectric sepa¬ 
rating the conductors. The Leyden jar is a familiar example. In 
this case a glass jar, coated inside and out with tin-foil, gives the two 
conductors which are separated by means of the glass of the jar as a 
dielectric. The capacity of circuits is usually measured by compar¬ 
ing the quantity of electricity which may be stored upon them with 
that of a standard condenser. The condenser usually consists of a 
box of insulating material in which are 
preserved a number of alternate layers 
of tin-foil, separated by paraffine paper 
or mica as an insulator, the paraffine 
paper serving in the condenser precisely 
the same office as the glass in the Ley¬ 
den jar. A condenser may be charged 
by connecting its terminals with the 
poles of a battery, the amount of elec¬ 
tricity stored being in proportion to the 
size of the condenser and the electro¬ 
motive force of the battery. 

The unit of capacity is the “farad.” 

Inasmuch as this unit is too large for 
ordinary work, condensers are usually made in fractions of one or 
more millionths of a farad, termed a microfarad. 

The standard condenser usually takes the form of a carefully 
finished box, having upon its top a series of plates that may be con¬ 
nected by means of plugs to respective divisions of the condenser. 
In fact, the apparatus very closely resembles a resistance or megohm 
box. An exceedingly convenient size is given in the illustration, 
Fig. 149, having a total capacity of one microfarad, subdivided into 
five parts of .5, .2, .2, .05, and .05 microfarad each. 

231. The different subdivisions of a condenser may be combined 
either in series, in parallel, or in the various combinations of series- 
parallel. Thus : supposing that C' C" C'", etc., be the respective capaci¬ 
ties of the various subdivisions of a condenser. They may be grouped 



Fig. 149. Standard Condenser. 





























































216 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


in parallel as represented by C -j- C" + C'" -f- C"" + etc. Under this 
condition the total capacity will be equal to the sum of the respective 
capacities. This condition may be expressed graphically as shown 
in Fig. 150. 



Fig. 150. Diagram of Condensers in Parallel. 


When the combination is made in series the joint capacity 
follows the law of the resistance of parallel circuits, the capacity 
being the reciprocal of the sum of the reciprocals of the respective 
parts. Analytically this is expressed by : — 


C = 


Y + N 

C C" 


+ 7^777 + 


c 


c 


rrrr 


+ etc. 


Graphically the relation may be indicated by Fig. 151. 


C' 


C" 


c 


m 


Fig. 151. Diagram of Condensers in Series. 


Further combinations may be made by uniting the parts of 
a condenser in any of the possible series-parallel arrangements. 
Such combination may be expressed either symbolically or graphi¬ 
cally. For example, one combination of a three-part condenser is : — 

r^u s^rtr 
/ _i V V 

C" + C'" ’ 

or graphically, Fig. 152. 



Fig. 152. Diagram of Condensers in Series-parallel. 


Thus, with two divisions in a condenser, four combinations may 
be made ; viz. : — 


C', C", C' + C" 


C'C" 


? 


and 


C’ + C"' 



















ELECTKICAL INSTRUMENTS. 


217 


With three divisions fourteen combinations may be made, the 
possible combinations increasing in a geometrical ratio with the 
number of parts of the condenser. 


WATTMETERS. 

232. The wattmeter forms one of the most valuable measuring 
instruments at the command of the electrician ; for by its use the 
total energy delivered at any point of a circuit may be measured, 
irrespective of the variations in potential and current. Instruments 
of this kind are divided into two classes, known as the Indicating 
Wattmeters and the Inte¬ 
grating Wattmeters. In¬ 
struments of the first divis¬ 
ion are typified by the Wes¬ 
ton Wattmeter and the Sie¬ 
mens Electro-dynamometer, 
which have been already de¬ 
scribed. Their province is 
simply to indicate the in¬ 
stantaneous value of the 
product of the volts and 
amperes traversing any part 
of the circuit. The second 
class, or integrating instru¬ 
ments, embrace nearly all 
the various devices known 
as electric meters, of which 
the Thomson Recording Wattmeter is a representative example. 
These instruments do not indicate instantaneous values, but inte¬ 
grate the total energy delivered to the circuit during the time through 
which they are attached to it. Thus the readings of these devices 
are in watt-hours or watt-minutes. To obtain the average instan¬ 
taneous value of the energy, the reading of the instrument (if in 
watt-hours) must be multiplied by 3,600, and divided by the time 
expressed in seconds during which the meter has been in circuit. 

233. The Thomson-Houston Wattmeter. — One of the most 
valuable forms of wattmeter is that devised by Professor Thomson, 
and is shown in Fig. 153. 













































218 


THE ELECTRICAL TRANSMISSION OF ENERGY. 



It consists of an iron frame carrying two heavy coils of wire, 
through which runs a light shaft attached, near its base, to a copper 
plate revolving between the poles of three magnets. 
The shaft also carries a coil of fine wire placed inside 
of the coarse wire coils. This instrument is therefore 
an electrical motor, in which the coarse wire coils form 
the field, the fine wire coils the armature, the rotation 
of the shaft being proportional to the product of the 
current in the coarse and fine wire coils, which, in turn, 
is proportional to the total quantity of electricity and 
to the pressure in circuit. The rotation of the copper 
disk between the poles of the magnets experiences a 
constant retarding force, which tends to check the mo¬ 
tion. The dial at the top serves to register the rota- 

ng. 154 . tion of the shaft, and is calculated to give readings in 
Short-circuiting watt-hours. Thus this instrument sums up the entire 

Key. . ... 

energy which flows through a given circuit between 
any two intervals of time at which readings may be taken. 

234. Keys.— To complete a set of testing instruments, a num¬ 
ber of keys should be provided for readily manipulating the circuits. 
The most important keys are the short-circuiting key, the reversing 
key, and the discharge key. See Figs. 154, 155, and 156. 

By means of the short-circuiting key, the galvanometer coils may 
be closed upon themselves at the instant of opening the circuit, thus 
checking the oscillations of 
the needle, and tending to 
render the instrument dead¬ 
beat. 

By means of the revers¬ 
ing key the direction of the 
current in a given circuit 
may be quickly and conven¬ 
iently changed. 

The discharge key is a 
device for connecting the 
condenser alternately with the charging battery and the galvanom¬ 
eter, and is a necessary adjunct for all capacity tests. 

235. The Magneto. — The apparatus termed “ a magneto,” 



Fig. 155. Discharge Key. 












































ELECTRICAL INSTRUMENTS. 


219 


frequently used in making tests of electrical machinery, is a very 
convenient rough-and-ready instrument. It consists of a small box, 
Fig. 157, carrying a bell fur¬ 
nished with a small alternat¬ 
ing current dynamo. By 
means of a crank at the 
side of the box the arma¬ 
ture of the dynamo can be 
rotated, thus gener¬ 
ating an alternating current. 

If the circuit of the machine 
is closed, the current flows 
through the bell, and by 

. , Fig. 156. Reversing Key. 

causing the bell to ring, 

gives indication that the circuit is continuous. The magneto is 
chiefly used to detect low insulation. For this purpose the little 
generator is wound to be able to ring the bell through a resistance 
of from twenty to twenty-five thousand ohms. It thus forms a very 
handy and convenient detector for the purpose of determining short 
circuits or defective insulation. After considerable practice with 
a particular instrument, it becomes quite possible to make a rough 

approximation of the resistance 
of a circuit by judging from the 
strength and clearness of the 
ring which is given. 

236. Ground Indicators. — 
Important lines carrying heavy 
currents should, as a matter of 
safety, be provided with con¬ 
stantly acting telltales to in¬ 
stantly indicate any fault in the 
insulation. The most simple of 
these contrivances is arranged 
in the following manner. Two 
similar incandescent lamps, of an 
appropriate voltage to be fully illuminated when placed in parallel 
across principal conductors, are connected in series as shown in Fig. 
158, at L and L' (p. 220). 



Fig. 157. The Magneto. 


rapidly 






































































































































220 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


ku 




B 


Under these circumstances the lamps will burn at a dull red. As 
long as the circuit is completely insulated, no current will traverse 

the wire f The galvanometer, or bell, 
~~ gives no indication, and the aspect of the 
_ two lamps is identical. If now, however, 
a leak occurs at any other point of the 
line, a current will flow through f. One 
of the lamps, therefore, will find itself 
shunted by the circuit through the earth, 
and will consequently burn less brightly, 
while the light of the other lamp is aug¬ 
mented. 

237. Upon lines carrying alternating 
currents, an analogous arrangement can be 
used ; and as it is inadvisable to perma¬ 
nently ground any part of the circuit, it is 

Continuous Current frountl Indicator. better t0 interpose ill the grOUlld wire a 

switch, by means of which connection may 
be made whenever it is desired to test the insulation of the line. 
Moreover, it is advisable to make the test-wire a part of the primary 
circuit of a transformer, in the secondary of which the telltale lamps 
are placed. The arrangement of this apparatus is shown in Fig. 159. 
238. These con- 




f 

A 


SNA 

/ V 

T 

-We 

WA4 

ft 




kk 









¥ 

" V 




trivances, however, are — 
defective to the extent 
that they do not give 
continuous and auto¬ 
matic indications of 
the insulation of the 
circuit, but require the 
presence of an opera¬ 
tor to obtain results. 

The following modifi¬ 
cation of the ground 
indicator may be used 
for alternating circuits, 
from which continuous indications can be obtained. The principle 
of this contrivance is shown in Fig. 160. 


)•» i_ 

c. 


** /*• 

C ( "'N 

/ ; 









Fig. 159. Ground Indicator for Alternating Currents. 





































ELECTRICAL INSTRUMENTS. 


221 



Fig. 160. 

Telephonic Ground indicator. 


Between the principal conductors two large metallic plates are 
connected, C and C', forming the armatures of a condenser. The 
other plates are connected to the ground by 
means of a wire, into which is placed a tele¬ 
phone, t. As long as the insulation remains 
perfect no current flows through the grounded 
wire. As soon, however, as a fault occurs, 
an alternating current is set up in the wire, 
which manifests itself by so loud a hum in the 
telephone as easily to be perceived throughout 
a large room. The sensitiveness of the tele¬ 
phone is sufficient to make this apparatus 
work successfully with condensers of very 
small capacity. 

239. The Boyer Speed Recorder. — 

The Boyer Speed Recorder, Fig. 161, is an instrument for obtaining 
instantaneous values of, and recording the curve of speed of any axle 
on any machine, and consists of a little rotary oil-pump supplied with 

a gauge, recording pencil, 
and a cylinder carrying a 
roll of cross-section pa¬ 
per, which is moved by 
clockwork. For determi¬ 
nation of car speed, indi¬ 
cations are obtained by 
attaching the machine by 
means of a belt to the car-axle, 
the motion of the axle being 
transmitted to the pump, and 
producing a pressure upon a 
piston attached to the pencil, 
thus causing the piston to rise 
and fall in proportion to the 
speed attained by the car. As 
a result, the instrument traces a 
curve, whose abscissae and ordi- 



Fig. 161. Boyer Speed Recorder. 


nates express, at any instant of time, the value of the car speed as 
a function of time. A curve, as described by this instrument, is 
given in Fig. 162 (p. 222). _ 














































































THE ELECTRICAL TRANSMISSION OE ENERGY. 


-999 


240. While the indications of the Boyer instrument give instan¬ 
taneous values for car speed, it is frequently of 
use to obtain the mean speed. Assume on the 
horizontal axis of the diagram any points A and 
B, between which it is desirable to obtain the 
mean speed. The time required for the car to 
go any short distance dx , at a speed b, is dx / b. 
Consequently, the total time required for the 
car to go between points A and B is equal to 
the — 

R dx 



V) 

Q 

Z 

O 

2 

o 

o 

o 

cm' 

CM 

h 

D 

O 

03 

< 

O 

< 

o 


O') 

<r 

O 

H 

O 


j : 


The distance traversed is B — A, hence 


B —A 


a 

v 

O 

^3 

- 

£ 


<N 

CO 


£ 


C B dx 
J A L 


is the true mean speed. 


The integral 


r 


B dx 
i b 


o 

$ 

H 

X 

H 

$ 

Q 

Ul 

a 

a 

3 

Gf 

U 

CO 

o 

z 

a 

< 

o 

L. 

O 

h* 

W 

bi 

H 


is the area of a reciprocal curve to that given by 
the Boyer indicator, between points A and B, 
which may be obtained as follows : — 

Subdivide the base-line of the curve given 
by the indicator into equal parts, and set off 
upon the ordinates drawn to these divisions a 
series of lines, whose length will be, respectively, 
equal to the reciprocals of the ordinates to the 
Boyer curve at each proper point. 

Drawing a curve from the vertices of these 
ordinates, a new curve is obtained, which is the 
reciprocal curve sought for. When the car stops, 
the value of the expression under the integral 
sign becomes infinity, which cannot be included in the calculation. 

























































































































METHODS OF ELECTRICAL MEASUREMENT 


223 


CHAPTER VI. 

METHODS OF ELECTRICAL MEASUREMENT. 

Art. 241. To the practicing engineer, the various methods of 
electrical measurement are chiefly valuable as affording a means 
of inspecting the condition of the circuit of a plant for the electrical 
transmission of energy, with a view to the determination of the per¬ 
formance, in order to afford information as to the possibilities of 
increasing efficiency or remedying defects. In every electrical 
circuit, there are five elements which are worthy of consideration. 
To the line may be attributed the properties of resistance, capacity, 
and inductance, while, having regard to the energy conveyed, there 
are the factors of potential and quantity of current. 

In strictly scientific investigation, all electrical quantities are, by 
means of the C. G. S. system, finally referred to fundamental units 
of length, mass, and time. For practical work, the more common 
commercial units are chiefly used, being readily deduced from the 
C. G. S. system. 

242. Electrical Intensity. — The amount of energy transmitted 
by electricity is always measured by the product of two factors, 
namely, electrical intensity multiplied by electrical quantity. Elec¬ 
trical intensity, pressure, potential, or electro-motive force, as it is 
variously called, is that property of electrical energy by means 
of which it is enabled to overcome resistance. While the foregoing 
synonyms have not quite a parallel significance, when used in the 
most exact scientific sense, the terms are usually regarded as inter¬ 
changeable for ordinary work. The commercial unit of electrical 
pressure is the Volt, and may be defined as that amount of electrical 
pressure which will produce a current of one unit of electrical quan¬ 
tity in a circuit having one unit of resistance in one second (or unit) 
of time. 

243. Electrical Quantity. — The unit of electrical quantity is 
the Coulomb , and is defined as the amount of electricity which 
will flow through a circuit having a resistance of one unit in one 



224 THE ELECTRICAL TRANSMISSION OF ENERGY. 

second of time, when the difference of electrical pressure between 
the ends of the circuit is one volt. 

244. Unit of Current. — As a corollary to the two preceding- 
units, a circuit having a resistance of one unit, and which, under a 
pressure of one volt, delivers in a second of time one coulomb of 
electricity, is stated to carry one unit of current. This unit is 
termed the Ampere. Usually all currents are measured in amperes. 

The coulomb defines electrical quantity, pure and simple, while 
the ampere conveys the idea of rate of transfer ; namely, one coulomb 
per second, the ampere differing from the coulomb by embracing; 
the idea of time. 

245. Capacity. — It is found that circuits of all kinds, and, in 
fact, all conductors and insulators, are capable of storing a certain 
amount of electrical energy ; and the ability to thus contain electri¬ 
cal energy is termed “capacity.” The unit of capacity is the Farad\ 
and is that amount of electrical capacity which, under an electrical 
pressure of one volt, is enabled to store one coulomb of electricity. 
Unfortunately for practical use, this unit is altogether too large ; and 
the Microfarad , or millionth of a farad, is the subdivision most com¬ 
monly employed. 

246. Resistance. — The unit of resistance is the Ohm , and is 
equivalent to the resistance of a column of pure mercury, one 
square millimeter in cross-section, 106 centimeters in length, at a 
temperature of 0° Centigrade. For practical purposes, units of 
resistance, in the form of resistance-boxes, as described in the last 
chapter, are commonly employed. 

247. The Watt. — The amount of energy transmitted during a 
given time by an electrical current is equivalent to the product of 
the electrical pressure multiplied by the quantity of electricity. To 
measure the power of doing work of a given current, gives rise to 
the employment of a derived unit called the Watt, equivalent to 
the product of the volts and amperes, precisely in a manner similar 
to the determination of mechanical work by means of the foot¬ 
pound. Thus the rate at which any machine is capable of dispens¬ 
ing energy is measured by the number of foot-pounds per minute 
that it is capable of delivering ; so, in an electrical circuit, the rate 
of doing work is equal to the number of volt-amperes, or “ watts ” 
per unit of time. 



METHODS OF ELECTRICAL MEASUREMENT. 


225 


248. Ohm’s Law. — In any electrical circuit, the generator may 
be regarded as a contrivance whereby, at one point of the circuit, the 
electrical potential may be raised ; and if, for the sake of illustration, 
electricity be regarded for the moment as a material substance, the 
pressure is rendered useful by the amount of electricity which may 
be set in motion against the resistance of the circuit. In every part 
of a circuit the amount of work expended is equivalent to the quan¬ 
tity of electricity that passes this portion of the circuit, multiplied 
by the fall of potential, or loss of pressure, that takes place within 
the part of the circuit under consideration. 

According to the law of conservation of energy, the amount of 
work done by the generator will be precisely equal to the sum 
of all the work delivered in the whole circuit. If E be the electro¬ 
motive force between any two planes in any circuit, R the resistance 
between the planes, and / the quantity of current flowing, in amperes, 
the relation existing between these quantities has been stated by Dr. 
Ohm to be : — 

R = —. (33) 

As above written, Dr. Ohm’s law only applies to steady, non-pul- 
sating currents ; but if the quantities E, /, and R be assigned values 
expressing the instantaneous effective electro-motive force, effective 
current and impedance of the circuit, having due regard to the posi¬ 
tive and negative effects of capacity and inductance, the formula 
becomes applicable to currents of all descriptions, whether continuous 
or alternating, and of whatsoever shape of wave. 

249. Kirchhoff’s Laws. — Kirchhoff has announced, under the 
form of two laws, principles that underlie many of the formulae 
employed in electrical investigation. 

First Law. — If any number of conductors meet at a point, and 
if all the currents flowing toward the point be considered as positive, 
while all those flowing away from the point be considered negative, 
and if equilibrium exists, that is, if the electrical potential at the 
point of junction remains steady, the algebraic sum of all the currents 
meeting at the point will be zero. Mathematically expressed : — 

2/= 0. (A4) 

Second Lazo. — In any network of electrical conductors forming a 
closed polygon containing varying currents, varying resistances, and 





226 


THE ELECTRICAL TRANSMISSION' OF ENERGY. 


varying electro-motive forces, the algebraic sum of all the products 
of the currents and resistances is equal to the sum of all the electro¬ 
motive forces, or mathematically : — 

2 I X R = 2 E. (35) 

Nearly all the formulae for electrical measurements are based upon 
the laws of Ohm and Kirchhoff; and while the demonstration of the 
succeeding formulae are not given in full, they may readily be deduced 
from the above cited laws by the ordinary algebraic processes. 

250. It is now proposed to consider the determination of the 
various electrical quantities in the following order : — 

Resistance. Capacity. 

Current Strength. Inductance. 

Electro-Motive Force. 

For the determination of these quantities, such a selection of 

methods is given as will enable the 
practicing electrician to choose an ar¬ 
rangement to fit the apparatus com¬ 
monly to be found in all electrical 
installations. In the methods given, 
careful consideration has been exer¬ 
cised to include only those which are 
of the greatest practical value, leaving 
laboratory methods and tests at one 
side, as not being suitable for the 
field-work of the electrical engineer. 

In all methods of measurement, it is necessary to compare a stan¬ 
dard unit with the unknown quantity, in order to ascertain the ratio 
which exists between the two ; and for this purpose it is essential to 
make use of some form of indicator, by means of which comparison 
between the standard and the unknown can be readily made. In 
most electrical measurements, the galvanometer is selected for this 
purpose. 

All of the instruments necessary to the following methods have 
already been discussed and described in the previous chapter. 

251. Measurement of Resistance. — First , by deflection. In 
Fig. 163, suppose G to be a galvanometer of any desired type, E a 
battery, or other generator of convenient voltage, and r a known 


E 



Diagram for Resistance by Deflection. 









METHODS OF ELECTRICAL MEASUREMENT 


221 


' resistance, such as may be readily found in a standard resistance-box, 
and that it is further desired to measure the value of some unknown 
resistance, R. Connect up the galvanometer battery and the known 
resistance r, as shown in Fig. 163 ; that is to say, with the galva¬ 
nometer, battery, and resistance all in series. Let G equal the resist¬ 
ance of the galvanometer, r the known resistance, and r' the resistance 
of the battery and the remainder of the circuit. In many cases, this 
latter quantity is so small in comparison with the unknown resist¬ 
ances, that it may be neglected. If E be the electro-motive force 
of the battery, and I the current in the circuit, a certain deflection d 
will be produced on the galvanometer. By Ohm’s law, 


1 = 


E 

G + d + r ’ 


I(G + / + r) = E. 


(36) 

(37) 


Now, for the known resistance r, substitute the unknown resist¬ 
ance R. Under these circumstances, suppose /' to be the current 
in the circuit, giving a new deflection d 1 upon the galvanometer. 


/' = 


E 

G + r' + R J 


/'(£ + *•' + R) = E. 


(34) 

(39) 


Solving for R, transposing, and arranging, — 

£ = j,X(G + r+r’)-(G + r’). (40) 

As the deflections d and d 1 are proportional to the currents I 
and /', d / d' is proportional to ///', and may be substituted for it, 
hence: — 

R = -ji {.G + r + U) (G -j- r ). ' (41) 

a 


252. The deflection readings on the galvanometer scale in de¬ 
grees have been used in the formulae. When the readings are small, 
or when no special accuracy is required, this assumption is suffi¬ 
ciently correct. When the deflections are of considerable magnitude, 
or when in using the scale readings, either of an ordinary galvanom¬ 
eter or of a reflecting instrument, great accuracy is desired, the 
tangent of d and the tangent of d' should be substituted for the 
actual reading in degrees. To measure resistance by this method, 
the resistance of the galvanometer, as well as that of the rest of the 
circuit, must be known, or neglected. 




228 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


The galvanometer resistance is usually given by the maker. 
Knowing the galvanometer resistance, and neglecting that of the 
battery and connections, — 


R - L (G + r) - G. 


(42) 


By adjusting the resistance r so that d'= 2d, the preceding 
formula is simplified. Under this condition equation becomes — 



( 43 ) 


When it is inconvenient to make d' equal 2d, simplification may 
be obtained by making d' any even multiple of d. 

253. The quantity rd, obtained by multiplying a known resist¬ 
ance r by the galvanometer deflection produced with the resistance r 
in circuit, is called the galvanometer constant, and is much used in 
making line-insulation tests. 

Thus a galvanometer, megohm box, and battery are joined up in 
series, and a deflection of d divisions is obtained with r ohms in 
circuit, rd being the constant. Any other high unknown resistances, 
R', R ", R"' , etc., now are substituted for r, giving deflection d', d", 
d"', etc. In case r is very small compared to R ', R ", R"', etc., the 
method of the inferred zero may be advantageously applied. For 
great accuracy tangent d, tangent d' , etc., should be used. In using 
a tangent galvanometer with methods in which only one deflection is 
concerned, it is best to make the deflection as nearly 45 as possible. 
If two deflection methods are employed, it is advisable to make them 
fall, as nearly as may be, at equal distances on either side of 45. If 
one deflection is to be double the other, then about 85 and 55 are 
convenient to employ. 

For such measurements a battery of constant electro-motive force 
must be used, or corrections for change in pressure introduced. 
There must also be no change in the external magnetic field, or a 
redetermination of the constant is necessary. 

254. Resistance by Wheatstone Bridge. — Resistance measure¬ 
ments by Wheatstone bridge are extremely simple. A battery is 
connected to the binding-posts, marked “ Battery,” of the testing- 
set, and the resistance to be measured connected to the posts marked 
“ x." In each of the bridge-arms a peg is inserted in the coils that 




METHODS OF ELECTRICAL MEASUREMENT 


99 Q 

tmd W KJ 


are estimated to furnish the appropriate arm resistance; and then the 
pegs in the rheostat are shifted about until the needle of the gal¬ 
vanometer fails to move, indicating that a balance has been attained. 
The resistance indicated by the rheostat, multiplied by the appropriate 
factor due to the ratio of the bridge-arms, gives the desired resist¬ 
ance. To secure the best results, however, it is advisable to follow 
certain conditions. 

Referring to Fig. 188, Chapter V., assume the letters attached to 
the various parts of the bridge to represent the resistances corre¬ 
sponding to each one. Make a rough measurement to obtain an 


D 



approximation to the value of x. Then make the resistance in the 

j (cr I 7/-^ 2 

arm d , as nearly as convenient, equal to V —--. It should not 

' r + x 

be less than this quantity, nor larger than G+x. 

The electro-motive force of the battery should be as great as is 
convenient, compatible with safety to the testing-set, and the re¬ 
sistance of the exterior circuit as small as possible. Though these 
conditions are theoretically desirable, they can be attained practically 
very rarely, and only within the middle ranges of the capacity of the 
testing-set. If manipulated with great care and considerable skill, 
the ordinary testing-sets can be made to measure a thousandth of 







































230 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


an ohm ; yet they are hardly reliable to so small an amount; so, if 
much accurate measurement on small resistances is to be done, re¬ 
course should be had either to the slide-wire bridge or to the differ¬ 
ential galvanometer. So far as manipulation is concerned, the use 
of the slide-wire bridge is precisely the same as the common Wheat¬ 
stone pattern. 

Measurement of Resistance by Ohmmeter and Differential 
Galvanometer have already been described in the account of these 

instruments in Chapter V. 

255. Resistance Meas¬ 
urement by means of Volt¬ 
meter.— To measure resist¬ 
ance by means of a voltmeter, 
the apparatus should be con¬ 
nected as shown in Fig. 164, 
in which R is the resistance 
to be measured, E the bat¬ 
tery or source of current, V 
the voltmeter, and r a known re¬ 
sistance. The voltmeter is first 
connected around the resistance r. 
Suppose, under these circumstan¬ 
ces, the readings of the voltmeter 
to be V volts. After this reading 
is obtained, the voltmeter should 
be connected in a similar manner 
around the resistance R to be 
measured. In the latter case, sup¬ 
pose the readings on the voltmeter 
to be V' volts, then, — 

V : V' :: R : r. 
rV 



R 




Fig. 165. 

Diagram of Resistance Measurement with 
Volt and Ammeter. 


X = 


V 


(44) 


By this method the measurement made by the voltmeter is the fall of 
potential through each resistance. As the electro-motive force is sup¬ 
posed to be constant, the fall is directly proportional to the resistance. 

256. Resistance Measurement with Volt and Ammeter. — 
A modification of the preceding method may be made, when no con- 














































METHODS OF ELECTRICAL MEASUREMENT 


231 


venient known resistance is at hand, by using, in place of the known 
resistance, an ammeter as shown at A in Fig. 165. In this method 
the current /, flowing in the circuit, is given by the reading of the 
ammeter; while the fall of potential E, through the unknown resist¬ 
ance, is given by the voltmeter. Thus two elements of Ohm’s 
formula are obtained, from which R may be readily calculated. 
Thus : — 

* = f- («) 

257. Small Resistance. — To measure very small resistances, 
the method indicated by the arrangement in Fig. 166 is to be used, 

mV 



which is practically the same as in the preceding instance, except 
that, owing to the very small difference of potential to be estimated, 
a milli-voltmeter, mV, must be substituted for the voltmeter, in 
order to obtain readings of sufficient accuracy. A battery E, or 
other source, supplies requisite current, that is measured by the am¬ 
meter A. The unknown resistance R is placed in series with the 
ammeter and battery. The milli-voltmeter is applied to the points 
B and C, between which lies the resistance to be measured ; the 






























































232 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


reading giving the fall of potential between B and C. Care should 
be taken to make good contacts at B and C, that there may be no 
errors from loss of pressure at these points, and the reading at A 
and m\ T should be simultaneous. A very essential and practical 
application of this method is its adaptability to the measurement of 
resistance of armatures of dynamo machines. For this measurement 
the arrangement shown in Fig. 167 should be adopted, in which the 
milli-voltmeter is clamped to opposite sections of the commutator, 
while the battery and ammeter are placed in series with the same 
sections. The milli-voltmeter should be connected directly to the 





sections, and not to the brushes, to avoid introducing the error of 
the contact resistance of the brush. 

258. High Resistance. — For measuring high resistance, the 
connections shown in Fig. 168 are preferable. In this case the 
battery E, voltmeter V, and key K are so arranged that the resist¬ 
ance to be measured, R, may be either included or excluded from 
the voltmeter circuit. For measurements of this kind, as high an 
electro-motive force should be used as practicable, it being under¬ 
stood that in any event the potential is not higher than the highest 
reading of the voltmeter. With this arrangement, supposing r to 
be the resistance of the voltmeter, two measurements are made ; 
first, with the switch closed, and then with the switch open. Sup- 
































































METHODS OF ELECTRICAL MEASUREMENT 


233 


pose V to be the reading with the switch closed, 
switch open ; then — 

* = a v - n 


V' that with the 
(46) 


259. A very convenient application of this method of measuring 
resistance occurs in making frequent trials of the insulation of high 
potential circuits. It is practical to make such tests with the line in 
full operation. The apparatus should be arranged as shown in Fig. 



169, in which the voltmeter V is connected first from one main, 
and then from the other main, to the ground. Under these circum¬ 
stances, if V equals the difference in potential between the two sides 
of the line, V the reading between either side of the line and the 
ground, and r the resistance of the voltmeter; then, representing 
the line insulation by R, its value is given by the equation — 


R = r 


(R-n 

V ' * 


(47) 


260. In the case of a dead ground, V = V, and, consequently, 
R = 0. In case there is no current in the main, a test-battery may 






































234 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


be added, and the connection made first to one side of the circuit, 
and then to the other, as shown in Fig. 170. 

As the resistances of the commercial voltmeter and milli-voltmeter 



Fig. 169. Diagram of Method of Measuring Insulation Resistance. 


vary from a fraction of an ohm to upwards of a megohm, this method 
may be used with great convenience and accuracy to determine all 
resistances that are commonly found. 



Fig. 170. Diagram of Test for Insulation. 


261. Insulation Resistance by the Method of Loss of 
Charge.—When it is desired to measure the resistance of insulation 
of a conductor having considerable capacity, this property may be 
utilized. For example : suppose a cable insulated at one end, having 







































































































METHODS OF ELECTRICAL MEASUREMENT 


235 


its sheath grounded. Charged by means of a battery, it acts as a 
condenser, storing a certain quantity of electricity. If, now, both 
ends be insulated, the charge slowly diminishes, due to leakage; and 
it is possible to estimate the resistance of the insulation by the 
rapidity of loss of charge during a given time. Let E be the 
respective potential of the cable at the moment of charge, and e 
the potential after a certain number of seconds, T, has elapsed. 

It can be shown, under these circumstances, that 


R = 


26.06 
r \ 

C log — 


( 48 ) 


e 

in which C is the capacity of the cable in microfarads per mile, and 
R its resistance of insulation in megohms per mile. The measure- 


E 



Fig, 171. Diagram of Resistance Measurement by Loss of Charge. 


ment of E and e is best made by means of an electrometer. In this 
case the apparatus should be arranged as shown in big. 171, in 
which E is the charging battery, G the electrometer, C the cable, 
M a commutator, and K a double key. The cable is charged by 
connecting it for one minute with the battery. It is then entirely 
insulated, and, by means of the key K, is placed in connection with 
the electrometer, and the motion of the spot on the scale observed 
for a period of one minute. The readings of the electrometer, at the 
beginning and end of the minute, give E and c. By means of the 


































236 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


electrometer, it is practicable to watch the image on the scale dur¬ 
ing the whole time of the observation, thus noting all that occurs to 
the cable during the process of the loss of charge. 

262. In the absence of an electrometer, the measurement may 
be made by means of a galvanometer, by connecting the circuit, as 
shown in Fig. 172. Under these circumstances, E and e are ob¬ 
tained by the deflection of the galvanometer at the beginning and 
at the end of the time T, and the capacity is calculated from the 
preceding formula. 

263. Measurement of Line Resistance. — The resistance of 
lines may be readily measured by means of the Wheatstone bridge, 
under either of the following three methods : — 

1. When the bridge can be grounded at one end and the line at 



Fig. 172. Diagram of Insulation Measurement by Loss of Charge with Galvanometer. 


the other, so thoroughly as to interpose essentially no ground resist¬ 
ance, and when no earth currents interfere with the measurement, 
good results can be obtained, the bridge measurement giving directly 
the desired resistance. 

2. When a second wire of known resistance can be joined from 
the farther end of the wire to be measured and returned to the 
bridge. Under these circumstances, the resistance given by the 
bridge is that of the sum of the two wires, from which that of 
the known wire must be deducted, in order to obtain that which 
is unknown. 

3. In cases where three wires, X, Y, and if, are accessible, all of 
which may have unknown resistance. X and Y are to be joined at 
the farther end, and the resistance measured on the bridge, giving an 



















METHODS OF ELECTRICAL MEASUREMENT 


237 


amount A. X and Z are then joined in a similar manner, and meas¬ 
ured, giving a resistance B. Y and Z are then joined and measured, 
giving resistance C. Under these circumstances, 


A + B-C 

2 

(40) 

y _ A + C — B 

2 ’ 

(50) 

7 _B + C — A 

9 

(51) 


264. Measurement of Ground Resistance. — The estimation of 
ground resistance could be accomplished similarly to the determina¬ 
tion of any other resistance, were it not for the fact that frequently 
earth currents from extraneous sources, or polarization set up by the 
ground plates themselves, tend to vitiate the results. If these per- 
turbating causes do not exist, the Wheatstone bridge may be used, 
and the resistance determined in the usual fashion. If two wires 
can be obtained, the measurement may be made as indicated in the 
preceding paragraph. If the earth currents are reasonably steady, 
an approximation to the true quantity may be obtained by making 
two bridge measurements ; one with a positive and the other with a 
negative current, and taking the mean of the results. Otherwise 
the ground may be treated as a battery, and its resistance determined 
by any of the methods for measuring battery resistances. 

265. Special Methods for Resistance Measurements. — The 
preceding methods for the determinations of resistance are adapted 
to all the general cases that will fall under the notice of the elec¬ 
trical engineer. For certain special cases, such as the measuring of 
galvanometer resistance and internal resistance of batteries, or other 
generators, some special methods are more expeditious and will now 
be noted. 

266. Galvanometer Resistance by Equal Deflection Method. — 
Connect up galvanometer G, shunt S, resistance known r, and bat¬ 
tery E of so low internal resistance that it may be neglected, as 
indicated in Fig. 173. Note the deflection of G. Now remove the 
shunt, and increase r to r', a second known resistance, until the same 
deflection is given by the galvanometer, then — 

G = (52) 

r 







238 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


This test is most accurately made by adjusting S, the resist¬ 
ance of the shunt less than G; the resistance r should be as large 
as possible, but not larger than — 


r' being the largest attainable resistance. Low resistance battery 
power of sufficient quantity should be provided to give the deflection 
as nearly as possible at the angle of maximum sensitiveness. 

267. Galvanometer Resistance by the Wheatstone Bridge. 
Thomson Method. — Arrange the apparatus as shown in Fig. 174. 
Vary the resistance in the arm a or d , until the deflection on the 


G 




Fig. 173. Diagram of Resistance by 
Equal Deflection. 


Fig. 174. Diagram of Galvanometer 
Resistance. (Thomson’s Method.) 


galvanometer G remains the same, whether the key k be up or 
down, then the value of G, the resistance of the galvanometer, is — 


G 



(53) 


268. This test has the merit of being entirely independent of 
battery resistance, and of being very easily made. To attain the 
greatest accuracy, a should be about one-tenth of G, and b ten times 
as large as G Vary d until it is nearly correct, and then change 
the battery power so that the final deflection shall be, as near as 
possible, at the angle of maximum sensitiveness of the galvanometer. 
Adjust d till the deflection remains unchanged on pressing the key. 

269. Galvanometer Resistance by Condenser. — The connec¬ 
tions for this method are shown in Fig. 175, in which G is the gal¬ 
vanometer, C the condenser, E the necessary battery furnished with 
the key K, and S a shunt that can at pleasure be placed around the 
galvanometer. The condenser is charged with the battery, and then 


























METHODS OF ELECTRICAL MEASUREMENT 


239 


discharged through the galvanometer, giving deflection d. The con¬ 
denser is again charged and discharged through the galvanometer, 
when shunted with a resistance S, giving a second deflection d', 
then — 


d 


E 

G 




d r _ EGS 

d _ S 
d' G + S ’ 

If 5 can be made so that d' = dj 2, then G = S. 


(54) 

(55) 



Fig. 175. Diagram of Galvanometer Resistance by Condenser. 


270. Measurement of Battery Resistance by Voltmeter. — 
In Fig. 176 are given the connections for measuring battery resist¬ 
ance with a voltmeter. Suppose the battery to have an electro-motive 
force E. K is an appropriate key, and r a suitable known resistance. 
When the key K is open, the reading on the voltmeter indicates the 
potential of the battery. Upon closing the key K, the voltmeter 
indicates the difference in potential e existing between the ends of 
the resistance r. Under these circumstances, the resistance R of 
the battery is found from the equation, — 

E — e 


R = r 


e 


(56) 




















240 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


271. Galvanometer Resistance by Deflection. — Connect the 
galvanometer to be measured in series with a known resistance r, as 
indicated in Fig. 163, obtaining the deflection d. Replace r by a 
second known resistance r', quite different from r, giving a second 
deflection d '. Then, in formula (41), substitute r' for R, and solve 
for the value of G, obtaining — 


G = r ' d '~ r f . (57) 

d — d 

272. Battery Resistance by De¬ 
flection. — If the galvanometer resist¬ 
ance be known, and two known re¬ 
sistances are at hand, the preceding 
method may be used to measure bat¬ 
tery resistance. The connections are 
made as already described, the battery 
occupying the place of the unknown 
resistance. The known resistances are 
successively interposed in the circuit, 
the corresponding deflections obtained, 
and the necessary substitution made in 
formula (41). 

273. In general, equation (41), in¬ 
volving six variables, of which two, d 
and d', are always measurable, may be 
used to determine any one of the re¬ 
maining four, provided the other three 
are known, or may be neglected. 

274. Battery Resistance by Condenser. — One of the best 
methods for the measurement of battery resistance is that involving 
the use of a condenser, for the reason that, while the connections are 
simple, the battery remains almost constantly upon open circuit, and 
is, therefore, free from errors due to polarization. The connections 
are shown in Fig. 177. A circuit is formed, comprising the battery 
E, the resistance of which, R, is to be measured, the condenser C, 
the galvanometer G, two keys k and k', and a known resistance r, 
arranged to shunt the battery. These are connected as shown, so 
that by depressing the key k the condenser may be charged through 
the galvanometer G, giving a deflection d on the galvanometer, cor- 




K 



Fig. 176. 

Diagram of Battery Resistance 
by Voltmeter. 


















METHODS OF ELECTRICAL MEASUREMENT 


241 


responding to E , the electro-motive force of the battery. If now, 
while the key k remains closed, the key be also depressed, the bat¬ 
tery is shunted through the resistance r; the potential at the poles 
of the battery falls to a value e given by the equation — 


e = E 


r 

R + r* 


(58) 


and a new deflection d' in the contrary direction is now obtained on 
the galvanometer, serving to measure the quantity E — e. As the 
deflections are proportional to the electro-motive force, — 


whence — 


E _ d . 
E — e d" 



d 

7 ' ; 


R = rX 



(59) 


If the resistance r is so arranged that d' =dj 2, then R = r. (60) 


C 



Fig. 177. Battery Resistance by Condenser. 


275. Battery Resistance by Equal Deflection. — The equal 
deflection method for galvanometer resistance may be applied to 
determine battery resistance. The connections are shown in Fig. 
173, in which R is the battery resistance to be measured, S a shunt 
of known resistance around the galvanometer G, and known resist¬ 
ance r in series with R and G. The circuits being connected as 
indicated, a deflection d is obtained on the galvanometer. 5 is then 
removed, and r increased to r\ until the same deflection is obtained. 


R = S X 


r 

r — 


r 


r+G' 



Then, 





















242 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


276. 5 should not be less than R ; r + G should not be larger than 
s/G X (G + r' ), r' being the greatest attainable resistance. The de¬ 
flection should be arranged to fall nearly at the angle of maximum 
resistance sensitiveness. 

277. Measurement of Potential Differences. — The most sim¬ 
ple method of measuring potential differences is by means of a volt¬ 
meter ; the instrument being directly connected to the poles of the 
generator, and the reading of the needle indicating at once the de¬ 
sired voltage. As various instruments are made to cover a range 
from .00001 of a volt to 10,000 volts, they are amply sufficient for 
all ordinary practice. 

278. In the case of the Weston instruments, if the polarity of 
the generator be unknown, the instrument may also serve as a pole- 
finder ; for if, on connecting the instrument, the needle is deflected 
toward the right, the binding-post on the right hand is the positive 
pole. If the needle should be deflected entirely across the scale, 
indicating that the potential difference is greater than the instru¬ 
ment is designed to measure, it is advisable to use one having a 
greater range. Yet, at the same time, by introducing an additional 
resistance into the voltmeter circuit, a reasonable approximation to 
the correct voltage may be obtained. For example : supposing volt¬ 
meter reading to 150 volts be the only one at hand, and it is desired 
to measure in the neighborhood of 600 volts. 

Let A=the greatest number of volts to be measured. 

Let e — highest reading on the scale of the instrument at com¬ 
mand. 

Let r =the resistance of this instrument, and 

^L=the additional resistance necessary to make it read E 
volts, then — 

R = r E ~ e . (62) 

e 

Under these circumstances, when R ohms are added to the voltmeter 
circuit, the readings on the scale of the instrument must be multi¬ 
plied by the factor Eje. 

279. It is seldom possible to add the exact quantity R ohms to 
the voltmeter circuit. Supposing R' ohms to be the nearest approxi¬ 
mation to R that can be secured, then the scale readings of the volt- 

R '-f r 

meter must be multiplied by-to give correct values. 






METHODS OF ELECTRICAL MEASUREMENT 


243 


280. Measurement of Electro-Motive Force. The Condenser 
Method. — The arrangement of the apparatus for measuring elec¬ 
tro-motive force by the condenser method is indicated in Fig. 178, in 
which G is the galvanometer, E the battery, or generator, to be 
measured, e the standard cell with which comparison is to be insti¬ 
tuted, C the condenser, and S a shunt around the galvanometer. 
This method consists in charging a condenser having a capacity of 
about one-tenth microfarad, by means of the standard cell, and then 
discharging it through the galvanometer, and noting the deflection d. 
The condenser is now to be charged by the generator whose electro¬ 
motive force is to be measured, and again discharged through the 
galvanometer. 

A second deflection d' is obtained, the deflections being propor- 



pg c 



VftflflOJUt 

s 

Fig. 178. Measurement of Electro-motive Force by Condenser. 


tional to the electro-motive forces producing them ; and if m be the 
multiplying power of the shunt, 


E .. d' j-. med ' / fi o\ 

_ = m X -— ; E = —— . (b6) 

e a A 

281. Measurement of Electro-motive Force. Wheatstones 
Method. — The standard cell e is to be joined in series with a galva¬ 
nometer and any known resistance, giving a convenient deflection d. 
The resistance is now to be increased by an amount r ohms, and a 
second deflection d' is obtained. The generator to be measured is 
now substituted for the standard cell, and the resistance of the cir¬ 
cuit so adjusted that the deflection d is repeated. Additional resist¬ 
ance, r ohms, is now added to the circuit, until the deflection d' is 
again obtained. Under these circumstances, the relative electro¬ 
motive forces are directly proportional to the additional resistances 
required to repeat the deflections, — 


e : E 





r 


( 64 ) 
























244 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


The first resistance should be as large as convenient; and the added 
resistance should be about double the original in order to get the 
best results. 

282> Lumsden’s Method. — Join the standard cell e and the 
generator to be measured, E, with the galvanometer G and the resist¬ 
ance r' and r, as shown in Fig. 179. 



Fig. 179. Connections for Lumsden’s Method. 


Adjust r until no deflection is observed on the galvanometer. 
Under these circumstances, — 

e : E :: r ': r ; 



(65) 


283. Measurement of Current Strength; — To measure the 
amount of current flowing in a given circuit, the direct reading 



ammeter forms the most convenient instrument. Current strength 
is measured by interpolating instruments directly in the circuit, the 
readings on the ammeter giving the volume of current. 

284; If the volume of current be too great for the instrument at 
hand, there are three methods for making the requisite measurements. 
A circuit may be arranged as shown in Fig. 180, in which the am¬ 
meter forms a shunt in connection with another circuit r. Under 


























METHODS OF ELECTR/CAL MEASUREMENT. 


245 


these circumstances, knowing the resistance r, and the resistance of 
the ammeter, which is always to be found marked upon the case 
containing the instrument, the quantity of current flowing through 
the two branches of the divided circuit can be readily calculated by 
the formula for divided circuits, and the total current obtained by 
adding the respective quantities found in the branches. Suppose an 
ammeter having a maximum reading of “a" amperes is required to 
read to A amperes ; let r be the resistance of the instrument, r' 
the resistance of the shunt to be added; then, — 



( 66 ) 


The scale reading must be multiplied by A/a. 

As ammeters are always very low resistance instruments, great 
care must be taken to determine accurately the multiplying power 
of the shunt, and particular pains taken to see that no unknown or 
variable resistance is introduced in the various contacts. 

285. Measurement of Current Strength by Voltmeter. — If 
the total resistance of the circuit or any portion of it be known, 
the measurement of the current strength may be made by means of 
a voltmeter. If, for example, the terminals of a voltmeter be con¬ 
nected across a circuit including a known resistance of r ohms and 
a reading of V volts be obtained, two quantities in the general equa¬ 
tion of Ohm’s law are given, from which the current strength may 
be calculated. By this method very large currents may be measured 
by the use of the milli-voltmeter. For this purpose arrange a circuit 
as shown in Fig. 166, containing a copper bar or strip, the resistance 
of which is known or can be approximately calculated. 

The terminals of the milli-voltmeter are to be applied to two 
points of the strip, and the fall of potential taken by means of the 
milli-voltmeter between these two points. 

Supposing the conductor to have a resistance of r ohms, and the 
reading of the milli-voltmeter to be E volts, the strength of the 
current / will be — 

/=—. (67) 


The objection to this method lies largely in the difficulty in deter¬ 
mining the resistance of the part of the circuit included between the 
terminals of the milli-voltmeter. 




246 


THE ELECTRICAL TRANSMISSLON OF ENERGY. 


286. Measurement of Current Strength. Differential Gal¬ 
vanometer Method. — In one half of a differential galvanometer 
G, Fig. 181, is placed a standard cell e, and known resistance r. 
Knowing the electro-motive force of the cell, and the resistance g 
of one half of the galvanometer, and r the resistance of the rest of 
the circuit, the current flowing may be calculated. The current to 
be measured is now passed through the other half g' of the galva¬ 
nometer, and r varied to r', until the needle remains at zero. If the 
two coils of the differential galvanometer have equal resistance, the 
value of the unknown current is given by equation (68). 


/ = 



( 68 ) 


Should the two sides of the galvanometer be unequal, the pre¬ 
ceding result must be multiplied by the ratio of the two sides. This 
ratio may be determined by passing the current from the standard 
cell simultaneously through both halves of the instrument, and vary¬ 
ing the resistance of the respective circuits until equilibrium is pro¬ 
duced. The desired ratio is then evidently the ratio between these 
resistances. If the unknown current is very large, a shunt may 
be placed in this circuit and the multiplying power introduced in 
equation (68). 

287. Slide-Wire Method. — In Fig. 182, AB is a wire of known 
resistance per unit of length, with a slide at B. The current to be 
measured is passed through this wire in a direction BA. The galva¬ 
nometer standard cell and slide-wire are joined as indicated, so that 
the electro-motive force of the standard cell will oppose that of the 
current to be measured. The slide is then moved until the gal- 

€ 

vanometer remains at zero. Under these circumstances, / = - (69), 

r being the resistance of AB, and e the electro-motive force of the 
standard cell. 

288. Measurement of Electrostatic Capacity. — The most ac¬ 
curate and convenient method of measuring electrostatic capacity is 
to compare the unknown capacity to be estimated with that of a 
standard condenser. The arrangement of the circuits are given in 
Fig. 183. 

Supposing the capacity to be measured is that of a cable, the 
apparatus is so arranged that either the condenser or cable, by 



METHODS OF ELECTRICAL MEASUREMENT 


G 




Fig. 182. Diagram of Current Strength by Slide Wire. 


J52 


z^zi 


V-S 


A 



1I 



Fig. 183. Diagram of Circuit for Capacity Measurement. 













































248 THE ELECTRICAL TRANSMISSION OE ENERGY. 

means of a double key, may be charged from the same battery, and 
discharged through the galvanometer. Under these circumstances, 
the relative capacities are proportional to the deflections produced 
on the scale of the galvanometer. These deflections must be multi¬ 
plied by the proper factor in case the galvanometer is shunted to 
bring the readings within the limit of the scale. 

289; If a Ballistic galvanometer be employed, the scale readings 
can be used without correction. If an ordinary galvanometer is used, 
or one in which provision is made for checking the motion of the 
needle, a correction for the errors thus introduced must be made. 
This correction may be obtained by observing the first swing of the 
needle to the right, giving, for example, a deflection d ', then the 
second swing also to the right, giving the deflection d ". The true 

deflection on the scale is ob¬ 
tained from the equation 

d = d' + 1 ~ ■ (70) 

Should the deflections given by 
the discharge of the cable and 
that of the standard condenser 
be sensibly equal, no correction 
is needed. In cases where the 
cable or line to be measured is very long, or has very large capacity, 
it will not discharge itself instantly ; and one of the succeeding meth¬ 
ods must be employed in place of the above. It is also customary, 
in order to obtain uniform results, to allow the electrification by 
the battery, both of the condenser and that of the capacity to be 
measured, to proceed for a certain definite length of time, usually 
for one minute. 

290. Thomson’s Method. — The connections for Thomson’s 
method for estimating capacity are shown in Fig. 184. 

The resistances of two adjacent branches of a Wheatstone bridge 
are replaced by the capacity ;r to be measured on one side, and a 
standard condenser of appropriate capacity C on the other, while the 
remaining arms a and b are wired as in the cut. These capacities 
are then charged from the same battery during the same time, and 
are then simultaneously discharged through the galvanometer by 



Fig. 184. Diagram of Circuit in Thomson's Method. 


























METHODS OF ELECTRICAL MEASUREMENT 


249 


means of an appropriate key. When the resistances a and b are so 
adjusted as to produce equilibrium, and the galvanometer indicates 
no deflection, then 

/ Vr 

(71) 


x = 


Ca 


in which ;r is the capacity to be measured, and a and b the known 
resistance of the bridge-arms. 

291. Gott’s Method. —The method here indicated is in some 
cases more convenient to apply. The capacity to be measured 
and the standard condenser C are mounted in series, as shown in 
Fig. 185, arranged so that they may be charged from the battery 



E by means of the key K', and discharged through the galvanometer 
by the key K. The resistances a and b are adjusted until no deflec¬ 
tion is obtained on the galvanometer by closing the key K. Under 
these circumstances, using the preceding notation, — 

* = — . (72) 

For these two methods it is advisable that the standard con¬ 
denser and the capacity to be measured should have the same di¬ 
electric, as otherwise the different rate of absorption of different 
dielectrics may cause error. 

292. Divided Charge Method. — If a charged condenser be 
attached to a second condenser having no charge, the charge which 


























250 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


is in the first condenser will distribute itself between the two in pro¬ 
portion to their relative capacities. Thus, if a standard condenser 
containing a known charge be placed for a few seconds in communi¬ 
cation with a capacity to be measured, and then if the residual 
charge in the standard condenser be determined, the unknown 
capacity can be calculated. Thus, if C' be the charge in a con¬ 
denser of a capacity C which is connected to an unknown capacity 
C", the quantity C ! " which will remain in C will be — 


C" = C’ X 


C" = C X 


C 


C" + c 
C' — C'" 


c 


/// 


(73) 

(74) 


293. The Localization of Faults. — Three kinds of faults are 
likely to occur in electrical lines : — 

First. — The conductor under consideration may be broken and 
entirely insulated from the other conductors and from earth. Under 

these circumstances, the resistance 
of the wire is infinite, or is equal to 
the original insulation of the circuit. 
If the previous capacity of the line is 
known, the localization of the fault 
may be determined by measuring the 
capacity of the wire ; that is to say, 
the capacity from the testing-station 
to the point of rupture of the con¬ 
ductor. If the line is one having 
considerable capacity per unit of length, so that slight changes in 
length give rise to relatively large variations in capacity, this method 
of localization has a fair degree of accuracy. 

294. Second. — If the faulty conductor is either crossed with a 
neighboring conductor, or with the earth, so that the fault has essen¬ 
tially no resistance, it is comparatively easy to locate its position by 
measuring the resistance of the conductor to the point of the cross. 
If the original resistance, or resistance per unit of length, be known, 
the localization of the fault becomes a mere matter of proportion 
between the measured resistance and that per unit of length. 

295. Third. — Faults with resistance. Most frequently, how¬ 
ever, considerable resistance is encountered at the fault itself; and in 


A_ x _ F V B 

R 

T 

A_ x _ F V B 

R 

▼ ** 

Fig. 186. Diagram of Blauier's Method. 










METHODS OF ELECTRICAL MEASUREMENT 


251 


order to locate the position of the fault, some method must be 
devised either to eliminate or to measure this amount. Blavier’s 
method is shown in Fig. 186, in which A is the testing-station, B 
the end of the line, F the fault having a resistance R, and x and y 
the respective resistances of the segments into which the fault 
divides the line. The operation consists in measuring the resistance 
from A, when B is insulated, being the resistance of the part of the 
line x plus the resistance R of the fault, giving a quantity — 

.v + R = R'. ‘ 


The end of B is then grounded or connected to a return conductor, 
and a second measurement taken, giving a quantity, — 


x —(- 


yR 


= R", or x -f- 


= R 


i// 


y + R - 7 ’■ ” ' 1/R + 1/y 
Also it is essential to know the original resistance of the line, — 


x + y = R'". 


From these three equations the value of can be calculated, and is 
shown to be given by the equation — 


x 


= R" — V(R' — R") (R'" — R") ; 


(75) 

and y = R'" - R" + V(R' - R") (R'" - R "). (76) 

296. The Overlap Method. — A convenient modification of 
the foregoing method may be employed when the measurements can 
be made from each end of the faulty line. Under these circum¬ 
stances, A measures when B is insulated, and B measures when A is 
insulated. In the latter case, when B insulates, a measurement from 


A gives — 


x -\- R = R'. 


When B measures, A insulating, — 

y + R — R", and 

x + y — R'", the original resistance. 

Then the value of x is found from equation - 

R m + R" - R' 
x = ---; 

R”' — R" + R' 

y = -2-• 

The location of faults existing in submarine cables presents problems 
of peculiar difficulty, owing to the fact that the rupture of the cable 


(77) 

(78) 











252 THE ELECTRICAL TRANSMISSION OF ENERGY. 

usually admits sea-water to the interior, thus allowing a saline solu¬ 
tion to come in contact not only with the core, but with the sheath 
of the cable, thus forming a battery that is capable of giving quite a 
perceptible current in the core of the cable. Many ingenious and 
successful methods have been presented for the determination of 
faults of this kind, for full description of which the reader is referred 
to works particularly devoted to the subject of electrical testing. 

297. Loop Test. Murray’s Method. -— When both ends of 
the faulty conductor are accessible to the same testing-station, as, for 
example, a cable on reels, or if another perfect conductor can be 
obtained for testing-purposes, the loop-test forms one of the most 
accurate and convenient of methods. The connections should be 



Fig. 187. Circuits for Murray's Method. 



Fig. 188. Circuits for Variey’s Method. 


made as shown in Fig. 187, in which a and b are the arms of a 
bridge at the testing-station ; F the location of the fault ; and ^ and 
y represent the respective resistances of the segments into which F 
divides the conductor from c and E (the ends of the bridge-arms) to 
the fault. cF is the faulty conductor, and EP the perfect one 
looped with it. AB and AE are adjusted until equilibrium is 
attained, then — 

b y = ax. ( 79 ) 

Assume R to be the total resistance of the loop, then — 


R — x + y and y = R — x, 


substituting this value of y in equation (79), and solving for x, _ 

Rb 

b -j- a 


x 


(80) 
































METHODS OF ELECTRICAL MEASUREMENT 


253 


b and a should be made as high as possible to give great range of 
adjustability. A heavy battery should be employed, especially if 
the fault has high resistance. The galvanometer should have a 
resistance of not more than five times that of the circuits under 
test. 

298. Varley Method. — This is a modification of the preced¬ 
ing loop-test, of which the connections are shown in Fig. 188. In the 
diagram BC, BA, and AE are the respective arms of the bridge, 
having the resistances a , b, and d , corresponding in notation to Fig. 
138 ; a and b are the fixed resistances of the bridge, while d is the 
variable arm. F is the location of the fault, while x and y are respec¬ 
tively segments of the line extending from E and C. The resistance 
°f x + y = R is supposed to be known. The variable arm d is 
adjusted until the galvanometer indicates equilibrium. 


a\b\\y\ (d -|- x) ; 


by 

a 


INSULATED 


INSULATED 


X 



299. To attain the greatest accuracy, a should be as small as 
possible, but not less than 

Gx 

G + x’ 

b should be so high that when d is a single unit out of balance there 
will be a perceptible movement of the needle. 

300. Localization of Crosses. — To localize the position of a 

cross between two lines, the following method is sometimes conven¬ 
ient. Arrange connections between the lines, as shown in Fig. 189, 
in which AB and CD are the crossed lines. Adjust the arms of 
the bridge a and b and the resistance r to produce equilibrium. 
Then x -\- y = br / a. (83) 

301. Rearrange the apparatus, making connections as indicated 
in Fig. 190, by placing the battery between A and the junction of 



















254 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


INSULATED 



Fig. 190. Diagram for the Location of a Cross. 


the bridge-arms, without making other changes, then ax = by , when 
r — 0. From these two equations 

x = -t- X b JL. (84) 

a -J- b a 

302. Measurements of Coefficients of Inductance. — The de¬ 
termination of the coefficients of inductance may be easily made 

by means of a Wheatstone bridge, 
a condenser, and a variable non- 
inductive resistance. The appa¬ 
ratus should be mounted as shown 
in Fig. 191, in which A and B are 
the constant arms of the bridge, 
R the variable arm, S the variable 
non-inductive resistance, and R'L 
the inductance to be measured, of 
which R! is its ohmic resistance to a continuous current, while C is a 
condenser placed as a shunt across the arm of the bridge, in which 
S and R'L are inserted in series. The object of S is to bring the 
capacity required to balance the inductive resistance within reason¬ 
able limits. The balance is obtained by adjusting the mutual values 
of C, S, and R until no deflection is produced on the galvanometer 
when the battery circuit is inter¬ 
rupted. Under these circum¬ 
stances, if A and B are equal, 
the value of L is found, from 
the expression L — CR" 2 (84), in 
which R" is equal to the sum of 
5 and R'. 

303. The value of this method 
may be extended over greater 
ranges by giving A and B any 
desired ratios, as in ordinary 
bridge measurements. The aux¬ 
iliary resistance 5 is required to 

adjust the capacity within reasonable values to balance the induc¬ 
tance. If, for example, 

L has a value of .4 Henrys, 

R 1 has a value of 10 Ohms, 

C must be equal to .01 of Z, or 4000 M.F. 



Fig. 191. Circuits for Measuring Inductance. 


























METHODS OF ELECTRICAL MEASUREMENT. 


255 


Such a capacity would be beyond ordinary apparatus. By in¬ 
creasing R 1 to 1000 ohms by the addition of the adjustable resistance 
S, C becomes equal to .4 M.F, an easily obtainable capacity. 

304. The Measurement of Self-Inductance with an Alternating 
Current of Known Period. — When an alternating current of known 
frequency can be obtained, the determination of the coefficients of 
inductance may be made; the apparatus needed being an alternating 
current dynamometer, a direct current ammeter, and a non-inductive 
resistance of known value. These instruments are all set up in series 
with the generator, in such a way that the current of known fre¬ 
quency may flow through the inductive resistance to be measured, 
and the known resistance. The direct current ammeter should be 
provided with a switch whereby it may be short-circuited at pleasure. 
The necessary measurements then consist in measuring the fall of 
potential with the alternating current dynamometer around the induc¬ 
tive resistance of which the inductance is desired, and also around 
the non-inductive resistance. A continuous current is then substi¬ 
tuted for the alternating current ; the amount of continuous current 
being varied until the dynamometer gives the same fall of potential 
across the known non-inductive resistance as was obtained in the 
first measurement. The amount of the continuous current is then 
obtained by reading the ammeter ; and a measurement of the fall of 
potential across the inductive resistance, when supplied with a contin¬ 
uous current, is made with the dynamometer. The first and second 
dynamometer readings E and E 1 across the terminals of the induc¬ 
tive resistance give two E.M.Fs, the first of which is required to over¬ 
come the ohmic resistance plus the inductance, while the second is 
that required to overcome the ohmic resistance only. Knowing the 
amount of current /, in the second observation, and the frequency n> 
in the first, the value of L is determined from the expression — 



(85) 


305. This method is subject to error, due to the current taken 
by the dynamometer, which must be of sufficiently high resistance 
as to be negligible in comparison with the resistance to be measured. 

306. Measurement of Mutual Inductance. —The preceding 
method may be employed to measure the coefficient of mutual 
inductance M\ of two coils. Let R x and R 2 be the respective ohmic 





256 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


resistance of the coils, and L v and L 2 the respective coefficients of 

inductance. First connect the two coils in series, and measure the 

total inductance by the above method, obtaining a value denoted by 

L. Then connect the coils in opposition, and again measure the 

total inductance, and denote the quantity thus obtained by L". It 

can be shown that _ . _ , 0 

L' = L x + Z 2 + 2 M; 

also, L" — L x + Z 2 — 2 M ; 

hence, M = —— . (86) 

4 

307. Measurement of Mutual Inductance. —To determine the 
mutual inductance of two coils, a circuit should be arranged, as indi¬ 
cated in Fig. 192, in which the first coil A is placed in series with 



Fig. 192. Circuit for Measuring Mutual Inductance. 


the key K, and the battery P, and resistance R t , while the second 
coil B is placed in series with the galvanometer G and the resistance 
R 2 . Between the points a and d a condenser C is placed as a shunt. 
The other extremities b and c of the resistances R t and R 2 are placed 
in series. Opening and closing the key K produces induced currents 
in the coil B, giving deflections on the galvanometer which are pro¬ 
portional to M — CR X R 2 . By varying the capacity of the con¬ 
denser, different deflections are obtained, which have the following 
relation : 

A/7 _ ( 7V IS A/J _ f ” V 7S 

(87) 


M— CR x R 2 M— C'R x R 2 


d 


d' 


in which C and C 1 are the different condenser values, and d and d' 
the different corresponding deflections, from which the coefficient M 
is obtained by equation — 


when d reduces to zero. 


M= CR X R 2 . 


( 88 ) 
















METHODS OF ELECTRICAL MEASUREMENT 


257 


MEASUREMENTS ON ALTERNATING CURRENT CIRCUITS. 

i 

308. Measurements of Potential. — Measurements of potential 
upon alternating current circuits may be readily made by means of 
hot wire voltmeters, Siemens dynamometers, or electrostatic volt¬ 
meters. With the electrostatic instruments sufficient range can 
usually be obtained so that pressure determinations on any ordinary 
alternating circuits may be made directly by interpolating the volt¬ 
meter across the circuit. With the Siemens dynamometers or the 
Cardew voltmeters, the instruments rarely have sufficient range to 
permit of a direct determination ; and recourse is usually had to the 
method of using a small step-down transformer, by means of which 
the voltage of the circuit is reduced in proportion to the ratio of the 
windings of the transformer. Under these circumstances, to obtain 
the actual voltage of the circuit, it is necessary to multiply the read¬ 
ings of the voltmeter by the ratio of transformation. 

309. Measurement of Current. — The determination of current 
quantity may be made upon alternating circuits by means of a 
Siemens dynamometer, a Thomson balance, or other instruments 
of similar construction and based upon parallel principles. The 
operation consists in inserting the measuring instrument directly in 
the circuit, and obtaining the desired readings. In measurements 
of this kind, as well as those described for obtaining the pressure of 
the circuit, the readings of the instruments indicate what is termed 
“ the effective current, or potential,” being the square root of the 
mean square of the instantaneous values of current or pressure. 

310. Measurement of Power. — The method to be used in 
determining the power transmitted by an alternating circuit depends 
upon whether the circuit under examination is inductive or non- 
inductive. In the case of non-inductive circuits, it is simply neces¬ 
sary to measure the virtual pressure and virtual current, as already 
described, taking the product of these two quantities as the amount 
of power transmitted. When the inductance of the circuit is con¬ 
siderable, the power measurements may be made with an electro¬ 
dynamometer, either of the Siemens or the Kelvin type — the coarse 
wire coils being connected in series with the circuit, while the fine 
wire is placed across the mains. Under these circumstances, to 
secure accuracy, the following conditions are essential : — 


'258 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


First. The ratio of the inductance of the instrument to its 

resistance must be very small. 

Second. The period of vibration of the movable coil must be 
very great compared with the period of the circuit. 

Third. When an auxiliary transformer is used for reducing the 
voltage, the current required for the fine wire coil 
must be very small. 

311. Power Measurement by Two Voltmeters. — Messrs. 
Ayrton & Sumpner are the authors of the following method for the 
measurement of power of an alternating current by the employment 
of two voltmeters and a non-inductive resistance. The circuit is 
arranged so that the inductive resistance of the circuit and the non- 
inductive resistance “r” are placed in series with each other. Then, 
by means of two voltmeters, the fall of potential across the inductive 
resistance e lf and across the non-inductive resistance e R , is measured. 



Fig. 193. Three-Ammeter Method. 


The total fall across both resistances is also measured and denoted 
by e. 

The power transmitted by the circuit, denoted by W watts is 
then, — 2 . 2 2 

W =-^. (89) 


2 r 


Method employing Three Ammeters. — J. A. Fleming is au¬ 
thority for measuring the power in an alternating circuit by the 
employment of three ammeters, as arranged in the accompanying 
illustration, Fig. 193. The inductive resistance is supposed to be 
placed at MN, and the known non-inductive resistance r, while the 
ammeters are shown at A lt A 2 , A 3 . The reading of the ammeters 
gives three currents, from which the power in watts, represented 
by W, is obtained from the formula, — 


W= r - (A 2 - A 2 - / 3 2 ). 


(90) 








METHODS OF ELECTRICAL MEASUREMENT 


259 


Measurements on Polyphase Current Circuits. 

312. Diphase Circuits.— Case 1. — To determine the power 
transmitted by diphase circuits, two conditions must be considered. 

First. — Circuits containing four wires. Under these circum¬ 
stances, each circuit may be measured separately and entirely inde¬ 
pendent of the other circuits, and the results considered either 
alone or in conjunction with the results obtained from the second 
circuit. 

< 

Second. — Three wires with a common return. 

To determine the power delivered by such a circuit, two watt¬ 
meters are necessary, and should be placed with the coarse wires in 
series with the separate parts of the component circuits, while the 
fine wire is placed across the common return and each of the exterior 
wires. 

313. Triphase Currents. — Measurements upon triphase cir¬ 
cuits for current and potential may be made in the same manner as 
described for ordinary alternating circuits. To determine the power 
delivered by a triphase circuit, three cases must be considered. 

314. Case 1. —Where the circuits supply non-inductive resist¬ 
ance without current lag. Under these circumstances, the power 
is equal to V3 times the product of the current intensity in each 
circuit, multiplied by the effective difference of potential between 
the wires. This method holds good indifferently, whether the 
arrangement of circuit is the star or the triangle method. 

315. Case 2. — Case of equal lag and equal current. One watt¬ 
meter is arranged with its coarse wire in series on one of the circuits ; 
and two readings are made with the fine ‘wire successively, between 
the circuit under measurement and each of the other branches. The 
sum of the results thus obtained is the total power transmitted. 

316. Case 3. — The general method for any current and any lag. 

Two wattmeters are employed, arranged with the coarse wires in¬ 
serted in two of the three circuits and the fine wires placed respect¬ 
ively between the third circuit and the other two. The sum of the 
readings thus obtained gives the total power transmitted by the 
circuit. 

317. Eectrical Railway Testing. — By means of the foregoing 
methods the electrical engineer will be able to make such selection 






260 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


as to enable him to thoroughly investigate the electrical properties 
of any ordinary line construction. No data or methods are given, 
either for the examination of dynamo machinery or for the determi¬ 
nation of special factors, being beyond the scope of this volume. 
There remains, however, the special case of electric railway testing, 
which, having chiefly for its object the determination of the electrical 
properties of the conducting system, necessarily embraces within the 
measurements made for this purpose a large amount of data appli¬ 
cable to ascertaining the performance of the car-motors and the 
generating-station. A necessary adjunct to the examination of an 
electric railway plant is a reasonably accurate plan and profile of the 
entire line. If not already in existence, a transit survey may be 
rapidly made with sufficient accuracy, covering from ten to twenty 
miles per day’s work. The tangents may be run out with great rapid¬ 
ity by stadia measurements, the location and amount of all gradients 
being simultaneously determined by means of a grade-screw on the 
vertical circle of the transit. The curves may be rapidly located by 
chord deflections. A testing-car should now be provided, which 
should be equipped with the following instruments : an integrating 
wattmeter, a Weston voltmeter, ammeter, and milli-voltmeter, a Boyer 
speed recorder, a revolution counter, a stop-watch reading to quarter 
seconds, and a gong. A separate observer should be provided for 
each instrument, with appropriate note-books having numbered 
lines, so that all observations may be correlated by corresponding 
numbers. 

The instruments may all be appropriately arranged on the car- 
seats, being protected as much as possible against jarring by extra 
cushions and rubber springs. The voltmeter and ammeter are intro¬ 
duced in the motor circuit, so as to measure the amount of current 
and pressure. The wattmeter is similarly introduced, in order to 
integrate the total energy expended. The general connections of 
these instruments are indicated in Fig. 194. 

The speed counter is to be connected to the driven axle of the 
car, provided only one motor is used ; or if the car is a double motor 
equipment, one may be temporarily thrown out of service. The 
object of the counter is to determine the number of revolutions of 
the car-wheel, that, being multiplied by the wheel circumference, 
will give accurately the distance traveled by the car. Indeed, so 


METHODS OF ELECTRICAL MEASUREMENT 


261 


accurate is this method of measuring that repeated trials over a six- 
mile stretch of road have checked within an error of fifteen feet. It 
is obvious that, to prevent error, the counter must be attached to 
a driven , not a driving axle. The Boyer speed-recorder may be 
attached to the same axle, and, being a self-recording instrument, 
may be placed in charge of the same observer who records the 
counter. The instruments being in readiness, the car is arranged 
to start from one end of the line, one of the observers being detailed 
to strike the gong at the instant each line-pole passes the center of 


TO TROLLEY 


GROUND 



the car. At each gong-stroke each observer records the reading of 
his particular instrument. 

318. The records will then show readings corresponding to suc¬ 
cessive points along the line, as marked by each pole, consisting — 

1st. . . . Time in seconds 4th. . . . Wattmeter 

2d. . . . Voltmeter 5th. . . . Revolution-counter 

3d. . . . Ammeter 6th. . . . Pole number 

On the conclusion of the run, the information from each of these 
records should be plotted as a curve upon the sheet of profile-paper 
containing the plan and profile of the road, as developed from the 
previously mentioned surveys. 









































262 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


319. Contemporaneously with the trip of the inspection-car, sta¬ 
tion voltmeter readings should be obtained, either by a self-recording 
instrument, or by five-second interval observations. These should 
likewise be plotted as a curve on the profile-sheet. The line should 
now be short-circuited at the extreme end, through sufficient resist¬ 
ance not to overload the generator, but yet to permit a heavy current 
to pass through all the wiring, and the inspection-car again sent 
over the road, hauled by horses, so that the car will take no current. 
During this trip voltmeter readings should be made at each pole, 
together with a repetition of the station voltmeter observations. 
These readings should likewise be plotted on the profile-sheet. 
From this test, the behavior of the line under a steady load may be 



Fig. 195. Diagram of Test-Circuit for Electric Railway. 


contrasted with previous curves of variable load. During this trip 
the milli-voltmeter should be connected with the fore and aft wheels 
of the car. Then the readings of the instrument will indicate the 
fall of potential in the rails in each car-length, affording a ready 
means of detecting any discontinuity in the return current, such as 
poor bonding, etc. 

320. The examination may now be completed by measuring from 
the station the insulation and conductivity, jointly and separately, 
of the ground return feeder system and trolley wire. This is best 
accomplished by stringing a test-wire of about No. 14 or 16 gauge 
parallel with all the lines, and arranging the stations and testing- 
instruments as in Fig. 195. By this means, the line resistance, as 
well as the ground resistance, can be separately determined. A care¬ 
ful consideration and comparison of the curves to be developed from 


















METHODS OF ELECTRICAL MEASUREMENT. 


263 


this information will, from a maintenance standpoint, be richly re¬ 
warded ; for in this way only is it practicable to so thoroughly and 
carefully adjust the conducting system of a railway line to the load¬ 
ing thrown upon it, as to secure a proper distribution of energy with 
reference to the demands introduced by grades, curves, variation in 
moving load, and the demands caused by the stopping and starting 
of the cars, in order that the line and station shall work together 
harmoniously in the endeavor to attain a maximum efficiency. 

321. The Capacity of Aerial Lines. — Though the preceding 
methods are applicable to the determination of electrical quantities 
under all circumstances, when applied to the measurement of trans¬ 
mission lines, special precautions have sometimes to be taken. The 
capacity of an aerial line is a difficult quantity to measure, for the 
reason that lines of this kind are 

L _ 

usually not highly insulated, and 
for this reason will discharge them¬ 
selves in an extremely short period 
of time. It is possible, however, 
to obtain quite accurate results for 
aerial line capacity by arranging 
the circuits as shown in Fig. 196, 
in which AB is a lever pivoted at 
C, that by means of spring r is 
kept constantly in contact with the 
terminal a of the battery key M. 

The line L is brought to the center of this lever at C. A second 



K 


— )G 



Fig. 196. 

Connection for Measuring Capacity in 
Aerial Lines. 


key K is mounted in series with the galvanometer, the depression of 
which makes contact with the lever AB at B. It is apparent that 
the action of this key is to open the battery circuit and close the 
galvanometer circuit, approximately, at the same instant. The line 
is charged for one minute by closing the battery key M. Then, by 
depressing the key K, the battery circuit is opened and the line 
circuit closed through the galvanometer at the same instant. The 
readings of the galvanometer, in comparison with those of a stan¬ 
dard condenser, by any of the methods already given, furnish the 
necessary data for calculating the line capacity. This galvanometer 
reading however, must be corrected for two errors. 

322. First. — It is usually found that different readings are ob- 










264 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


tainecl when the line is charged with a positive current than when 
it is charged with a negative current. This difference is owing to 
the presence of the earth currents, which always manifest themselves 
upon aerial lines of any magnitude. Two deflections, therefore, ob¬ 
tained with currents of different sign, will differ by an amount due 
to the presence of such a foreign current. The deflections, therefore, 
must be corrected by subtracting or adding to the galvanometer read¬ 
ing obtained by the battery discharge the amount of deflection due 
to the earth current. This correction may be readily obtained by 
closing the galvanometer key with the battery key open for a few 
moments, and reading the deflection given by the earth current. 

323. Second. —The deflection obtained upon the galvanometer 
is not exact, unless the opening of the battery circuit and the closing 
of the galvanometer circuit occur at mathematically the same instant; 
and the apparatus can rarely, if ever, be adjusted to accurately accom¬ 
plish this. Therefore, usually the battery is short-circuited through 
the galvanometer for a very short interval of time. To determine 
the value of the error thus introduced, substitute for the line L three 
standard condensers, the capacities of which are known quite accu¬ 
rately to be in the ratio of 14, 2, and 4, and by closing the key K, 
measure the galvanometer deflections obtained with these conden¬ 
sers in the place of the line, exactly in the same way as the line 
measurement is made. If the source of error alluded to does not 
exist, the following relation would be true : — 

d' _ d" _ d" f 

1.5 2 4 ’ 

in which d\ d", d"\ are the respective deflections. If equality does 
not exist in the above equation, the following relation evidently will 

d r T x _ d" -f- x _ d"' -f- x 

1.5 ~ 2 ~ " ” 4 ~ ’ 

in which x is such a quantity as will satisfy the equation. From the 
known value of the standard condensers with which these readings 
are made, it is possible to calculate the value of „r, and thus deter¬ 
mine the error introduced by the momentary short-circuiting of the 
battery through the galvanometer. Having obtained this figure with 
standard condensers, it may be applied to correction of the galva¬ 
nometer reading, as obtained from the experiments upon the line. 








METHODS OF ELECTRICAL MEASUREMENT 


265 


324. An example may perhaps render the subject more clear. 
Suppose an aerial line, when tested with a positive current, to give 
a deflection of 73 divisions on the galvanometer scale, and with a 
negative current, of 113 divisions, also, that the deflection due to 
earth current is found to be 20 divisions. The true deflection on the 
galvanometer evidently then should be ^=73 + 20=113—20 = 93, 
the earth current evidently opposing the positive current. To intro¬ 
duce the second correction, assume three condensers, having the 
ratios of 1^, 2, and 4, to give on the galvanometer scale deflections 
of 72, 88, 152. In order that the three numbers representing the 
deflections shall stand in the same ratio as the capacity of the con¬ 
densers, it is necessary to subtract from each one 24. Correcting 
the line galvanometer de¬ 
flection by the same num¬ 
ber, the value of 69 re¬ 
mains as the true deflec¬ 
tion. 

325. The capacity of 
aerial lines in reference 
to the earth, as usually 
measured, is considerably 
greater than that which 
would be theoretically in¬ 
dicated. To account for 

the discrepancy between the measured figures and those given by 
theory, it is usually assumed that the insulators, poles, and cross- 
arms possess a sensible capacity which is inevitably measured in 
all trials made upon aerial lines. Confirmation of this hypothesis is 
obtained in the fact that in dry weather the line deflection falls, and 
agrees much more closely with the results indicated by theory. 

326. The Inductance of Aerial Lines. —The estimation of the 
inductance of aerial lines may be made by any of the methods given ; 
those that employ the Wheatstone bridge, as indicated in Fig. 197, 
being particularly convenient. The two parts of the line L and L' 
are looped into the station, L being connected to AB, one of the 
bridge-arms, and C connected to AC, the other. In the line L the 
variable resistance r, and variable condenser c are arranged, while 
the contact a represents the slide of the bridge, as, for this experi- 



Fig. 197. 

Circuit for the Measurement of Inductance on Aerial Lines. 






266 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


ment, a slide-wire bridge is a convenient piece of apparatus. After 
adjusting a to obtain a balance for constant current, the capacity of 
the condenser c is increased or diminished, until the needle of the 
galvanometer remains at zero on interruption of the current. The 
inductance of the line is then given by the expression, L=cr 2 . (91) 
327. It must not be forgotten that the line itself has always 
a capacity; so from the above expression the true inductance of the 
line is not obtained, but a quantity equal to L — \ CR 2 , in which R 
is the resistance and C the capacity of the line itself. To demon¬ 
strate this, suppose, in Fig. 198, the two parts of the line to be 


A £ B e C 





\ 




C, 

_ J 

/ 

V B 

i i 

\ 


Fig. 198. Diagram of Line Capacity. 


represented by AC and AjQ, and assume the line to be divided into 
n equal parts, AB, BC, etc., and AjB,, B^, etc. At each section 
of the line imagine a small condenser to be placed, whose capacity 
c { c 2 etc., is the capacity of the section under consideration. Repre¬ 
sent the resistance of each section by p, and the capacity of the con¬ 
denser at each point by </>. The condenser c x placed across the points 
AA] acts as an inductance of the value — <$>irp' 2 ) the next con¬ 
denser c 2 at BB t acts as an inductance of the value —</>(« —1 ) 2 p 2 , 
and so on for all the n sections into which the line is divided. All 
of the condensers are equivalent to an inductance of the value 
— cf> p 2 (1 +2 2 -f 8 2 -f. . . . -j- (« —1) 2 + // 2 ), but the sum of the squares 

of the numbers from 1 to n is 

n in -f- 1) (2 n -f- 1) 

6 ’ 

and the value of the inductance equivalent to the condensers is 

_ H ( U 1 ) 11 + 1 ) 

6 

As (f> = —, and 

71 

the preceding expression becomes 

_ 11 ( H T 1) 11 T 1) £^r, 2 




















METHODS OF ELECTRICAL MEASUREMENT 


267 


When » = oc , - (” + !) ( 2 ” + 1) = ^ 

and consequently the capacity of the line acts as an inductance of 
the value — £ CR 2 . Consequently the true value of the inductance 
of the line is obtained by adding to the value of Z, as given in equa¬ 
tion (91), the value of the negative inductance due to capacity, or 

L = c r 2 + i CR\ (92) 

C and R being measured by any desired method. 

328. Measurement of Mutual Inductance on Transmission 
Lines. — To estimate mutual inductance on a pair of lines, the appa¬ 
ratus should be arranged as shown in Fig. 199, in which L is the 
primary or inducing line, and. L' the circuit in which inductance is to 


r-4- 


B R A 


K K. P| 

L 

* 1 

a 







W 


Fig. 199. Circuit for Measuring Mutual Inductance on Aerial Lines. 


be measured. By means of the key K the primary line L is earthed 
through the resistance R ; an electrical impulse is sent through this 
line from the battery P that produces inductive effects on the other 
line L'. The grounds rr x , as well as the earths at the remote ends 
of the lines, must be entirely separate from each other. The deflec¬ 
tion produced on the galvanometer by the mutual inductance of 
the lines, and the charge of the condenser C, is proportional to 
M—CRR', C being the capacity of the condenser, R the resistance 
of the rheostat, and R' that of the line L'. By adjusting the 
rheostat and condenser till no deflection is observed, 

M = CRR'. (93) 

As earth currents are likely to give much trouble in obtaining the 
final balance, a small battery /, with an adjustable shunt, may be 
placed in L', and arranged to neutralize such disturbances. 












268 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


CHAPTER VII. 

CONTINUOUS CURRENT CONDUCTORS. 

PART I.—CONDUCTORS AND INSULATORS. 

Art. 329. Conductors; — When a quantity of positive electricity 
is placed upon any perfectly insulated body, it occupies for the first 
infinitesimal period of time, a small surface immediately surrounding 
the point of contact, and raises the potential of this surface. Very 
rapidly, however, the charge distributes itself over the entire sur¬ 
face ; bringing every point thereof to the same potential. As, by 
hypothesis, the body is perfectly insulated, this distribution of the 
charge can only take place by a passage of Electric Energy through 
the body itself. The property thus possessed by all substances to 
permit with varying degrees of rapidity the transfer of electrical 
energy is called conductivity. 

330. In some materials the distribution of the charge takes 
place almost instantaneously, while for others an extremely long time 
is required. Good conductors are those which permit the distribu¬ 
tion of the charge to take place with great rapidity, while those 
requiring a greater length of time are called poor conductors, or 
insulators. If the substance under consideration is in the form of a 
wire, one end of which is maintained at a higher potential than the 
other, a continual passage of electrical energy will take place from 
the end having the higher potential to that which is lower. This 
condition once established, the quantity of electricity stored on the 
surface of the wire remains uniformly distributed, and evidently a 
steady flow or current takes place. 

331. From experiment it is ascertained that wires of different 
material, of the same geometrical dimensions, submitted to the same 
differences of potential, transmit very different quantities of electricity 
during the same interval of time. The quantity, therefore, of elec¬ 
tricity which one substance, under precisely similar conditions, is 
able to transmit, compared with that of another, is a measure of its 
conducting power. 


CONTINUOUS CURRENT CONDUCTORS. 


269 


332; Resistance: Ohm’s Law. — Let E be the difference of 
potential maintained between the extremities of a conductor, and / 
the intensity of the current ; that is to say, the quantity of electri¬ 
city that passes any given cross-section in successive equal intervals 
of time; if R is the resistance of the conductor, then — 


/ = 


E_ 

R 


P E 

r ~T' 


KI = E. 


(94) 


With a given difference of potential E, I decreases directly in pro¬ 
portion as R increases, and also with a definite resistance R, I is 
directly proportioned to E. This is the famous law of Dr. Ohm, that 
thus unites by an algebraic equation the three most important elec¬ 
tric quantities. Be it noted, however, that Ohm’s formula, in this 
form, applies to steady and continuous currents only. 

333. The resistance R of a conductor depends not only upon 
the material used, but also upon its geometrical dimensions. It is, 
therefore, possible to express the resistance of any conductor as a 
function of its geometrical magnitudes, and of a coefficient depend¬ 
ing upon the physical constitution of the material employed. Dr. 
Ohm, further, established the proposition that the resistance of any 
conductor is inversely proportioned to the cross section S, measured 
normal to the direction of the current, and directly proportioned to 
the length / of the conductor, and to a coefficient p, which he de¬ 
nominated the specific resistance of the material. Thus, algebraically, 


R = ^ . 
S 


(95) 


The geometrical dimensions being easily ascertained, it is sufficient 
for the purposes of calculation to know p for the materials under 
consideration. Substituting in (94), — 


pi _ E 


(96) 


If p, /, S, and E are constant, S / I gives the current density per 
unit of area of the cross-section of the conductor. 

334. Specific Resistance. — The resistance offered by a unit 
volume of any substance, as compared with the resistance of a unit 
volume of any other substance, selected as a standard, is termed 
“ Specific Resistance.” As the metal silver has the least resistance 
of any now known, or in other words is the best conductor, it is 




270 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


usually selected as the standard. In English measures the cubic 
inch is the volume adopted for comparison, while in the C. G. S. 
system the cubic centimeter is used. Thus the absolute resistances 
of various substances would be the opposition offered per cubic inch 
or cubic centimeter, while the specific resistance is the ratio of the 
absolute resistance to the absolute resistance of silver. The value 
of the absolute and specific resistances of the chief metals will be 
found in Table No. 17. For wire work the resistance of a grain 

Table No. 17. 

Chemically pure Metals arranged in Order of Increasing Resistance for the Same 

Length and Sectional Area. 


Name of Metal. 

Resistance in Microhms 
at 0° Centigrade. 

Relative 

Cubic 

Centimeter. 

Cubic 

Inch. 

Resistance. 

Silver, annealed. 

1.504 

0.5921 

1. 

Copper, annealed. 

1.598 

0.6292 

1.063 

Silver, hard-drawn. 

1.634 

0.6433 

1.086 

Copper, hard-drawn. 

1.634 

0.6433 

1.086 

Gold, annealed. 

2.058 

0.8102 

1.369 

Gold, hard-drawn. 

2.094 

0.8247 

1.393 

Aluminum, annealed. 

2.912 

1.147 

1.935 

Zinc, pressed.. 

5.626 

2.215 

3.741 

Platinum, annealed. 

9.057 

3.565 

6.022 

Iron, annealed. 

9.716 

3.825 

6.460 

Gold-silver alloy (2 oz. gold, 1 oz. silver), 
hard or annealed. 

10.87 

4.281 

7.228 

Nickel, annealed. 

12.47 

4.907 

8.285 

Tin, pressed. 

13.21 

5.202 

8.784 

Lead, pressed. 

19.63 

7.728 

13.05 

German silver, hard or annealed . . . 

20.93 

8.240 

13.92 

Platinum-silver alloy (1 oz. platinum, 2 
oz. silver), hard or annealed . . . 

24.39 

9.603 

16.21 

Antimony, pressed. 

35.50 

13.98 

23.60 

Mercury. 

94.32 

37.15 

62.73 

Bismuth, pressed. 

131.2 

51.65 

87.23 


foot, or the resistance of a wire weighing one grain, and one foot in 
length, and also the resistance of a mil foot, or the resistance of a 
wire one mil (yoTo of an inch) in diameter, and one foot long, are 
convenient working quantities. Table No. 18 supplies this data for 
the most common metals and alloys, giving also the values of the 
gramme-meter, and millimeter-meter. 

335. It should be carefully noted that different specimens of 
apparently chemically pure metal give different resistance, that can 
only be accounted for on the supposition that the varying processes 




























CONTINUOUS CURRENT CONDUCTORS. 


271 


Table No. 18. 

Resistances of Metals for Grain-foot, Mil-foot, Gramme-meter, and Millimeter-meter. 

(Legal Ohms.) 


Name of metals arranged in order of 
increasing resistance for the same 
length and weight. 

Resistance of 
a wire 1 foot 
long, weigh¬ 
ing 1 grain. 

Resistance 
of a wire 

1 foot long, 

T uW.of 
inch in dia¬ 
meter. 

Resistance 
of a wire 

1 meter long, 
weighing 

1 gramme. 

Resistance 
of a wire 

1 meter long, 

1 millimeter 
in diameter. 


Ohms 0° C. 

Ohms 0° C. 

Ohms 0° C. 

Ohms 0° C. 

Aluminum, annealed. 

0.1074 

17.53 

0.0749 

0.03710 

Copper, annealed. 

0.2041 

9.612 

0.1420 

0.02034 

Copper, hard-drawn. 

0.2083 

9.83 

0.1453 

0.02081 

Silver, annealed. 

0.2190 

9.048 

0.1527 

0.01916 

Silver, hard-drawn. 

0.2389 

9.826 

0.1662 

0.02080 

Zinc, pressed. 

0.5766 

33.85 

0.4023 

0.07163 

Gold, annealed. 

0.5785 

12.38 

0.4035 

0.02620 

Gold, hard-drawn. 

0.5884 

12.60 

0.4104 

0.02668 

Iron, annealed. 

1.085 

58.45 

0.7570 

0.1237 

Tin, pressed. 

Gold-silver alloy (2 oz. gold, 1 oz. sil- 

1.380 

79.47 

0.9632 

0.1682 

ver), hard or annealed. 

2.301 

65.37 

1.650 

0.1384 

German silver, hard or annealed . . . 

2.622 

125.91 

1.830 

0.2666 

Platinum, annealed. 

2.779 

54.49 

1.938 

0.1153 

Lead, pressed. 

3.200 

• • • • 

2.232 

0.2498 

Antimony, pressed 

Platinum-silver (1 oz. platinum, 2 oz. 

3.418 

213.6 

2.384 

0.4521 

silver), hard or annealed .... 

4.197 

146.70 

2.924 

0.3106 

Bismuth, pressed. 

18.44 

789.3 

12.88 

1.670 

Mercury. 

18.51 

572.3 

12.91 

1.211 


The following specific data relative to the resistances of copper in various forms has received the 
sanction of the report of a committee upon wiring, appointed by the American Society of Electrical 
Engineers. 

Table of Values based upon Matthiessen’s Correct Standard. 


B. A. Units. 
0° C. 


Legal Ohms. 
0° C. 


Matthiessen’s Standard Meter-gramme, hard 


.1469 

.1453 

.1436 

.1420 


.02080 


.02034 

.000001652 

.000001634 

.000001616 

.000001598 


9.829 

9.720 

9.612 


Specific resistance of hard copper (1 cub. cent.) = 1634 (C. G. S. units). 
Specific resistance of soft copper (1 cub. cent.) = 1598 (C. G. S. units). 
Matthiessen’s Standard specific gravity of hard copper, 8.89. 

Resistance of hard copper is 1.0226 times that of soft copper. 
Resistance of soft copper is .9779 times that of hard copper. 

Legal ohm is equal to 1.0112 B. A. units. 

B. A. unit is equal to .9889 Legal ohms. 


of manufacture produce corresponding inequality in molecular struc¬ 
ture, sufficient to account for these discrepancies. Even with pure 
specimens, in special cases, a variation of 16 per cent in the same 




































272 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


metal tested at the same temperature has been noted. In ordinary 
commercial products the range of variation may naturally be still 
greater. 

336. Effect of Temperature. — Specific resistances, also, are 
functions of temperature. For pure metals, the resistance increases 
as the temperature is augmented. The formula representing the 
effect of temperature may be written — 


R t — R 0 (1 + at -f- /3/ 2 ), (fb) 

in which R t is the final temperature, R 0 the temperature at which 
the specific resistance is originally measured, and a and /3 are 
coefficients denoting the function of the specific resistance and 
temperature. For any purpose but the most exact calculation, the 
approximation, — 


Rt — Ro (1 + tt/< )> 


(98) 


is amply sufficient. The values of these coefficients are shown in 
Tables Nos. 19 and 20. For copper, formula (97) becomes (approxi¬ 
mately) — 


R t = R 0 (1 + .00387 / + .00000597 / 2 ). 


(99) 


Table No. 19. 

Value of a and ft in Formula Rt — R 0 (1 + at + ftt 2 ). 


Description of Metals. 

a 

P 

Pure Metals. 

Mercury. 

Platinum-silver. 

German silver. 

+ 0.003824 

+ 0.0007485 

+ 0.00031 

+ 0.0004433 

+ 0.00000126 

- 0.000000398 

- 0.000000398 

+ 0.000000152 


Table No. 20. 


Value of a in Formula R t = R 0 (1 + at). 


Description of 
Metals. 

a 

Description of 
Metals. 

a 

Silver. 

Copper . 

Gold. 

Aluminum . . . 

Platinum .... 

Iron. 

Tin. 

Lead. 

0.377 x 10 - 2 

0.365 x 10 - 2 

0.390 x 10 - 2 

0.247 x 10- 2 

0.453 x 10 - 2 

0.365 x 10- 2 

0.387 x 10 - 2 

Antimony .... 
Bismuth .... 
Mercury .... 
Alloy 2 Pt. + 1 Ag. 

2 Au. -f- 1 Ag. 

8 Pt. + 1 Ir. 
German silver . . 

0.389 x 10 - 2 

0.354 x 10 “ 2 

0.088 xio- 2 

0.022 to 0.031 x 10“ 2 
0.065 x 10 “ 2 

0.133 x 10“ 2 

0.028 to 0.044 x 10 “ 2 



























CONTINUOUS CURRENT CONDUCTORS. 


273 


337: Resistance of Dielectrics. — Experiment shows that there 
is a large class of bodies which permit of the transmission of elec¬ 
trical energy so slowly that they may be termed ;/< 5 w-conductors, 
insulators, or dielectrics. Generally speaking, the metals and solu¬ 
tions of the metallic salts may be classed as conductors, while all 
other substances fall in the category of insulators. There is, how¬ 
ever, much variation in the relative value of non-conductors as 
insulators. In electrical construction the property of high resist¬ 
ance is employed entirely to isolate, or insulate, electrical currents 
in such a manner as to confine the transfer of energy along the 
paths which it is desired to have it take. Insulators may be applied 
to conduct the circuits in one of two ways. 

338. First.— The insulating substance may be arranged as a 
series of supports to which the circuit is attached from point to 
point, in order to separate it entirely from electrical communication 
with other bodies. For this purpose dielectrics, such as wood, glass, 
porcelain, india-rubber, and their various compounds, are molded 
into appropriate forms, mechanically arranged to permit of the 
attachment of the conductor circuit to the insulator, and then the 
attachment of the insulator to the support designed to carry the cir¬ 
cuit, in such a manner as to electrically isolate the circuit by means 
of the insulators from the supports. The various forms of insulators 
for this purpose have been already treated in Chapter III. 

339. Second.— The insulating substance may be arranged as a 
uniform and continuous coating, so applied as to surround and en¬ 
velop the circuit from end to end, thus rendering additional support 
unnecessary, and allowing the circuit to be placed in proximity to the 
ground or other bodies, at the same time preserving the electrical 
isolation. For this purpose the various forms of india-rubber are 
the basis of nearly all insulating materials. It is usual to secure 
sufficient mechanical strength by covering the conductor with one 
or more layers of fibrous material, such as braid composed of hemp, 
cotton, or silk, or by wrapping it with sheets of paper or jute, or 
similar material. These fibrous coverings may be impregnated with 
insulating compound, either previous or subsequent to their applica¬ 
tion to the conductor. As an example, the cables manufactured by 
Siemens Bros, are covered with jute impregnated with ozokerite. 
The Farranti mains are separated by a number of layers of paper 



274 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


impregnated with a compound of black wax. The Edison conductors 
are embedded in their tubes in a special mixture of india-rubber and 
resins. The various forms of okonite, ozokerite, and india-rubber 
covered wires all depend upon protection consisting of various india- 
rubber compounds, each applied in a manner peculiar to the particu¬ 
lar manufacturer. 

340. The various forms of india-rubber, under the names of 
caoutchouc and gutta-percha, are most extensively used for cable 
insulation, although the melting-point of the latter is so low as to 
prevent its wide adoption. 

Gutta-percha is a material of varying composition, depending 
upon its mode of manufacture ; and, consequently, having a specific 
resistance varying between 25 X 10 12 and 500 x 10 12 ohms-centi- 
meter. By fairly good methods of manufacture and the employment 
of pure materials, a resistance of 200 x 10 12 ohms-centimeter, at a 
temperature of 24° C., may be obtained. Caoutchouc has also a 
varying composition and resistance. It is valuable, however, in its 
ability to resist heat. By submitting the substance to the process of 
vulcanization at 130° C., a temperature much higher than should 
ever be attained by the passage of the current, a valuable and dur¬ 
able insulator is obtained, having a resistance of 7500 x 10 12 ohms- 
centimeter. 

341. The variation in specific resistance of dielectrics under 
changes in temperature is very much more rapid and much larger in 
amount than those of metals. This variation can only be expressed by 
an exponential equation, R 0 = R t a' (100), a being a coefficient that, 
owing to the process of manufacture, has to be determined separately 
for each specimen of insulating compound. Experiments upon gutta¬ 
percha used in submarine cable work assign a value to it between 
the limits of 0.876 and 0.894. For caoutchouc, the value is less care¬ 
fully established, but probably lies between a =0.941 and a = 0.955. 
For a variation of between 12° and 15° C., on either side of a tem¬ 
perature of 24° C., the specific resistance is approximately halved or 
doubled. For other insulating materials, the processes of manufac¬ 
ture vary too widely to permit the establishment of temperature 
coefficients. Table No. 21 gives the specific resistance of some of 
the more common insulators. 

342. Line Leakage. — Where transmission lines are supported 


CONTINUOUS CURRENT CONDUCTORS. 


275 


Table No. 21. 


Specific Resistance of Insulators. 


Name. 

Resistance in 
Megohms 
per Cubic Cen¬ 
timeter. 

Name. 

Resistance in 
Megohms 
per Cubic Cen¬ 
timeter. 

Mica. 

84 x 10-6 

Olive oil. 

1 x 10-6 

Gutta-Percha. 

450 x 10-6 

Lard oil. 

.35 x 10-6 

Shellac. 

9000 x 10-6 

Stearic acid. 

350 x 10-6 

Ebonite. 

28000 x 10-6 

Benzine. 

14 x 10-6 

Hooper’s compound .... 

15000 x 10-6 

Wood tar. 

1670 x 10-6 

Paraffine. 

Paraffine oil. 

34000 x 10-6 

8 x 10-6 

Ozokerite (crude).... 

450 x 10 * 


upon molded insulators, as in the ordinary forms of telegraph lines 
and other bare wire installations, the resistance of the line insulation 
varies from time to time, depending upon the state of the weather, 
the cleanliness of the insulating surfaces, and the number of points 
of attachment of the conductor to the insulators. Owing to these 
indeterminate factors, it is impossible to predict or calculate, except¬ 
ing within very wide limits, the insulation resistance of such lines. 
Data for the probable resistance value to be expected from molded 
insulators will be found in Chapter III. For conductors which are 
entirely covered by insulating material, such as underground and 
submarine cables, the insulation resistance is much more exactly 
known, and usually operates under very much narrower variations. 
As there is no known substance that forms a perfect insulator, there 
is found, in the most carefully constructed lines, surrounded with 
the greatest amount of protection, a constant and quite 
perceptible electrical leakage taking place through the 
dielectric substances employed for insulation. Know¬ 
ing the specific resistance of the dielectric and the 
geometrical relations of the conductor and insulator, 
the probable insulation resistance may be quite closely 
calculated. Thus, in Fig. 200, consider the case of a 
cable having a central conductor of the radius R, 
surrounded by a layer of insulating material having a 
radius R, and of a specific resistance p, and let L be the length of 
the cable. The resistance of an infinitely thin layer of a thickness 
dR 2 of the insulator at a distance from the center of the cable 

will be pdR* 

2 7i -R X L ’ 



Section of Insulated 
Conductor. 

























THE ELECTRICAL TRANSMISSION OE ENERGY,\ 


and the resistance of the entire coating is obtained by integrating 
the previous expression between the limits R and R 2 , obtaining 


the value 



( 101 ) 


The portion p/2tt is a constant factor for any given dielectric, so if 
A represents this factor, and L be made unity, and the diameter 
of the core and cable be substituted for R and R 2 , the insulation 
resistance is given by the expression A log D / d. 

343. Distribution of Potential in a Conducting Circuit. — In 
the preceding paragraphs the relation expressed by Ohm’s formula 
has been considered as applied to a circuit having a uniform resist¬ 
ance, and subjected to the effect of a single unvarying electro-motive 
force. Such a simple state rarely exists in practice, thus making it 
necessary to now investigate the conditions which obtain under more 
complex relationships. Electrical circuits usually consist of a gener¬ 
ator of some description, the office of which is to impress upon the 
circuit an electro-motive force of sufficient amount to perform the 
work demanded ; a line of conducting material serving to connect 
the generator with the various receiving mechanisms employed to 
utilize the energy produced; and lastly, the receivers of various 
kinds, in which the transmitted energy is applied to useful work. 
An analysis, therefore, of the entire circuit separates it into three 
parts deserving of consideration. 

First. The generator, or source of electro-motive force. 

Second. The line, or conducting system. 

Third. The receivers. 

In each of these divisions a certain amount of electro-motive force 
is expended, being employed either to overcome the resistance of the 
separate divisions, or expended in the receivers. 

344. From a commercial standpoint, the expenditure of the elec¬ 
tro-motive force may be separated into two parts : — 

First. The amount necessary to overcome the resistance of the 
various parts of the circuit, in order to convey from point to point 
the necessary quantity of electricity. 

Second. The electro-motive force usefully expended in producing 
mechanical work, or the evolution of energy in such a form as to be 
commercially valuable in the receivers. 







CONTINUOUS CURRENT CONDUCTORS. 


277 


345. That portion of the electro-motive force expended in over¬ 
coming the resistance of the various parts of the circuit is, as will be 
subsequently shown, transformed into heat, which by radiation is dis¬ 
sipated and lost, so far as its commercial value in the receiver is con¬ 
sidered, excepting in so far as its employment for the purpose of 
transporting the current from point to point of the circuit be embraced 
in the term of commercial use. This energy used in overcoming the 
resistance of the circuit is frequently, though erroneously, termed 
“wasted energy ; ” for it is solely by virtue of the expenditure of this 
portion of the total energy of the circuit that the remainder of the 
energy is transferred from the point of production to the point of 
consumption. Inasmuch as there is no known substance possessing 
no resistance, every part of the circuit involves the expenditure and 
dissipation as heat of a greater or less quantity of electro-motive 
force, in order to transmit the necessary current. 

346. Transforming Ohm’s formula, IR = E is obtained, indicat¬ 
ing that the quantity of electro-motive force expended in the circuit 
is equivalent to the current, multiplied by the resistance of the 
conductor. 

If i, i', i", etc., be the currents in various portions of a circuit, 
and r, r ', r" , etc., be the resistance of the corresponding parts of the 
circuit, and e, e\ e" , etc., be the expenditures of electro-motive force 
in each of these corresponding parts of the circuit, the following 
relations hold : — 

ir +iV'+ i'V"+, etc. = e + /+ /'+, etc. = Sir = Se = IR = £, (102) 

the capital letters standing for the sum of the quantities represented 
by small type. 

In the above equations, great care must be taken to apply to each 
of the electro-motive forces its appropriate sign, in order that the 
summation may give the algebraic sum of the various electro-motive 
forces. Consider the example of a dynamo employed to charge a 
storage battery. Suppose that the dynamo furnishes a potential of 
12 volts, and is employed in charging 5 cells of storage battery, the 
total potential of which, when fully charged at 2 volts per cell, would 
amount to 10 volts. 

Suppose the resistance of the generator to be of an ohm, and 
that of the leads to be T b of an ohm, and the resistance of the storage 


278 THE ELECTRICAL TRANSMISSION OF ENERGY. 

battery At of an ohm. The total resistance of the circuit will then 
be x 5 o of an ohm, and through this the generator will be capable of 
transmitting a current of 24 amperes. The resistance of t 2 q of an 
ohm for the storage battery is made upon the assumption that the 
charging is commenced when the battery is entirely discharged, and 
that the cells only oppose to the passage of the current their ohmic 
resistance. As the charging proceeds, an electro-motive force is 
developed in the storage battery, which opposes that of the gener¬ 
ator, tending constantly, as it increases, to cut down the effective 
electro-motive force, thus reducing the amount of current flowing. 
When the batteries are charged to their normal rating, each one 
would furnish a counter electro-motive force of 2 volts, the 5 cells 
aggregating a total counter electro-motive force of 10 volts. Under 
these circumstances, the total effective resistance of the circuit would 
be \ ohm for the ohmic resistance of the generator, leads, and bat¬ 
tery, with a counter electro-motive force of 10 volts developed by the 
cells. Assuming the previous notation, e = 2, $e = 10, ZT = 12, R = j, 
the value of the current then becomes — 

f _ E—^e = 12 - (2 X 5) = 4 

R \ 

Thus, when the batteries are sufficiently charged to give a counter 
electro-motive force of 2 volts each, the current in the circuit would 
be reduced from 24 amperes to 4 amperes. If the charging be con¬ 
tinued, the electro-motive force of the ceils gradually rises more and 
more, until finally the opposing electro-motive force exactly balances 
that of the generator, and the charging automatically ceases. 

347. The most convenient way to represent the potential distri¬ 
bution in a complicated circuit is the graphical method, in which val¬ 
ues along the axis of Y be taken to represent the electro-motive 
force, and those along the axis of X represent the relative lengths 
and resistances of the different parts of the circuit. 

Thus, in diagram, Fig. 201 represents the previously cited exam¬ 
ple of a dynamo machine charging 5 cells of storage battery. On the 
right hand of the illustration the general circuit is indicated, AB 
being the lead from the positive pole of the dynamo to the storage 
battery, BC the battery, CD the negative lead returning from the 
battery to the generator, and DA the circuit in the dynamo machine. 
On the left hand of the figure, assume OY is the potential axis, single 






CONTINUOUS CURRENT' CONDUCTORS. 


279 


volts being represented to scale, as shown in the diagram. Assume 
OX as the axis of resistance, in a similar manner. Under the sup¬ 
position that the battery is charged to a potential 2 volts per cell, 
the total current flowing in the circuit will be 4 amperes, as previ¬ 
ously shown. Assume, also, that the resistances in the various parts 
of the circuit, named AB, BC, CD, and DA, are uniform through¬ 
out each of the separate parts, the current, of course, being constant 
throughout the entire circuit. The fall of potential in AB will then 
be n = e= .05 x 4 = .2 volts. Along OY lay off OY positively up¬ 
ward, to represent 12 volts, the total potential of the generator. 
From A lay off AB horizontally, equal to .05 of an ohm, the resist¬ 
ance of AB in the other diagram. Lay off BB' vertically, negatively 



Fig. 201. Diagram of Potential Distribution in a Simple Circuit. 

downward equal to .2 volts, and draw AB'; then AB' represents the 
distribution of the potential throughout the lead AB. Between B 
and C there is an ohmic resistance of .2 ohm, and a counter electro¬ 
motive force of 2 volts per cell, or 10 volts. The fall of potential in 
this part of the circuit will then, evidently, be e = .% x4 + 2 x 

5 = 10.8 volts. ’From B lay off BC, horizontally, equal to .2 ohms, 
and CC', vertically downward, equal to 10.8+ .2 volts. Join B'C', the 
line B'C' representing the distribution of potential throughout the 
battery. The fall of potential in the lead CD is calculated in a man¬ 
ner similar to that indicated for AB, and the fall of potential in 
the generator DA in the same way; and thus, in the left hand illus¬ 
tration, the irregular line AB'C'DA indicates, for each of the various 
parts of the circuit, the distribution of the generator potential. 





















280 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


348. The Effect of Leakage. — In the preceding section the 
lines AB' and CD in the left diagram represent the distribution of 
potential along the conductors AB and CD that unite the generator 
to the receivers. It is evident, from the reasoning and construc¬ 
tion employed, that these are straight lines, having equations of the 
form— y = ax j r b (108) 

and that throughout the entire length of each conductor a constant 
and uniform current existed. This condition can only be fulfilled by 
assuming that the conductors are perfectly insulated ; for, if the insu¬ 
lation is defective in any way, some electricity will escape sidewise 
between the conductors, and the current will be less at the point 
B than it is at A by this amount of leakage. Consider two points 
in the conductor, the first one at a distance from the origin, and 
the second at a distance x + dx. The electro-motive force acting 
between these points is dE , while the resistance of the conductor 
between them is rdx, when r is the resistance of the lead for unit of 
length. The current flowing between these points is then — 


dE 

rdx 


(104) 


If the conductors were perfectly insulated, this value would be con¬ 
stant throughout the entire length, and equation would be that of a 
straight line. If the conductor leaks, then more electricity enters 
every element at the point ar than leaves the element at the point 
;r + dx , the difference in the quantity which enters the element and 
that which leaves it going to supply the leakage. If r x be the insula¬ 
tion resistance per unit of length, r x jdx is the insulation resistance 
of the element dx, and the flow of electricity sidewise from this 

element is — , Edx 

- dl = . (105) 


Eliminating I by differentiating equations (104) and (105), and putting 


* 



E_ = d 2 E 
m 2 dx 2 


(106) 


But this is the differential equation of the arc of a catenary, 1 which 
when integrated gives rise to the equation — 

x x 

E — Ae m -f- Be m . (107) 


1 See Rankins’s Applied Mechanics , p. 175. 







CONTINUOUS CURRENT CONDUCTORS. 


281 


For ordinary transmission, lines of moderate length, well built, care¬ 
fully insulated and maintained, the leakage is so small that without 
sensible error it may be neglected. For very long lines, such as 
submarine cables or overland telegraph or telephone lines, the 
straight line assumption is not sufficient, and the catenary equation 
should be used. 

349. Conductance. — From Ohm’s formula, it appears that the 
resistance of any circuit is proportional to the geometrical dimen¬ 
sions of the conductor, and to its specific resistance. If R be the 
resistance of any conductor, the reciprocal of R, or 1 /R, gives a 
quantity which is appropriately denominated, “ The Conductance of 
the Circuit,” or a quantity to which the ability to transmit electrical 
energy is proportional. If, between the terminals of any generator, 
a number of conducting circuits be extended, having the resistance 
of r, r', r", etc., the conductance of each branch will be 1/r, 1/r', 
1 / r", etc. It is evident that the total conductance is equal to the 
sum of the conductances of the individual parts. Thus, representing 
by c, c' , c", etc., the individual conductances, and by C the total conduct¬ 
ing power of the circuit, C=c-\-c' -\-c", etc. But c , c', c", etc. ; are re¬ 
spectively equal to 1/r, 1/r', 1/r", etc., or the conductance is equal to 
the sum of the reciprocals of the individual resistances. As resist¬ 
ance is the reciprocal of conductance, the total resistance, therefore, 
of a number of branch circuits is equal to the reciprocal of the sum 
of the reciprocals of the individual resistances, or symbolically : — 


R = 


1 


l + b + 


7 ' 


// 


+ etc. 


(108) 


350. A graphic method of quickly determining the resistance 
of two branch circuits is given by Mr. Preece. 1 

Assume in the diagram, Fig. 202, the line AB drawn horizontally 
to represent the resistance of one of the branch circuits; lay off 
BC to the same scale equal to the other resistance, and at C erect a 
perpendicular CD equivalent to BC. Join A and D, and at B erect 
a perpendicular BE, which will, to the same scale, represent the joint 
resistance of the two resistances, AB and BC. By drawing the line 
BD, and dividing AB, BD, and RE, according to the proper propor¬ 
tional scale of each line, joint resistances may be easily found in the 


i See Manual of Telephony , by Preece and Stubbs, p. 164. 














11 n ' " n 111.11111111111 L 11111 m 11111111ili i 11111 i.Ijii 11 m i 


282 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


•y. I —‘ _ 

J> O' “ 


co 


^ following manner : Select upon AB a number representing 
L_\ one of the resistances ; in a similar manner, select upon 
\ • BD a number representing the other resistance. Lay 




\ 


\ a straight edge across these two points, and the num- 
\ ber given upon BE at the intersection of the straight 


\ 


\ 


\ 


edge with BE is the joint resistance of the two cir¬ 
cuits. The scale on AB and BE is a simple deci¬ 
mal scale of equal parts. The scale on BD is also 
\ a decimal scale of equal parts, and is related to 
\ the scales on AB and BE in the proportion of 
\ 1 : a/2. As all three scales are decimal, the 

\ significant figures on all of them may be 
multiplied or divided at pleasure by any 
v power of 10, and thus the diagram ex- 
\ tended to cover any desired range of re- 
\ sistance. The geometrical relation of 
\ the three scales is self-evident. In 
\ the case of several branch circuits, 

1111 .1 11 nIm 1 1 1111 1 1111 1 111111111 1 1111 1 11 nl ^ the joint resistances of any two 

may be found by the diagram, 
and then this value combined 
with the resistance of any one 
of the remaining branches. 
By a continuance of this 
process any number of cir- 
\ cuits may, by the dia¬ 
gram, be calculated. 
351. Distribution 
of Potential and 
Current in Branch 
Circuits. — The 
equations for 
distribution of 
potential and 
current so 
far given 
apply sim¬ 
ply to a 
















CONTINUOUS CURRENT CONDUCTORS . 


283 


circuit consisting of a single source of electro-motive force, intro¬ 
duced in a circuit consisting of a single conductor extending from 
pole to pole of the generator. In practice, however, actual installa¬ 
tions are usually very much more complex, frequently consisting of 
a number of generators placed at different points of a complex net¬ 
work of conductors, which ramify in all directions over the territory 
to be supplied. To determine accurately the description of poten¬ 
tial and current in a complicated network, is a matter of exceeding 
importance to the electrical engineer. While calculations of this 
kind are based on simple algebraic applications of the laws of 
Ohm and Kirchhoff, a complete solution of the distributing prob¬ 
lem is difficult of successful solution, owing to the fact that, while 
the principles are simple, the application of them leads, usually, to 
exceedingly complicated and intricate equations. Any network of 
circuits may always be resolved into one of four elementary cases. 

352. Case 1. — Is that of a simple circuit embracing a generator 
placed in a continuous, straight conductor, extending from one pole 
to the other of the generator without branches, and may be treated 
directly by Ohm’s law. 

353. Case 2. — This consists of a generator supplied with a 
circuit consisting of one or more branches, as shown in Fig. 203, in 
which E is the generator or source of electro¬ 
motive force, ab and ac the conductors from 
the generator to the points b and c, at which 
points the circuit branches or divides into e_±L 
two parts of varying resistance. Let E de¬ 
note the E.M.F. of the generator, and r e its 
resistance. Let r x be the resistance of ab 
and ac, and r 2 and r 3 the respective resist¬ 
ances of the two branches from b to c, then the combined resistance 
between be is — 



Fig. 203. 


[' 2 ; n] = 


X Vo 


r 2 T r 3 

The total resistance of the entire circuit R is, 

D , , ^2 X r 3 

R = r e + r x + 


(109) 


, ( 110 > 

^2 T~ r 3 

Denote the respective currents in the various parts of the circuit 
by i lt / 2 , and i 3 , as indicated in the diagram, then,— 







284 


THE ELECTRICAL TRANSMISSION OF ENERGY. 



E (r 2 r s) 

(in) 

h — 

f \T 2 T r \ r z T 

• 

Er s 

(112) 

l 2 — 

T r 'l r S T 


Er 2 

(113) 

h — 

f 2 T r ' l r 8 

h _ 

r* 

• 

(114) 


Here r\ — r e + r x . If there are n branches, n similar equations 
may be formed. 

354. Case 8. — This is indicated diagrammatically in Fig. 204, 
in which there are two sources of electro-motive force, E x and E 2 . 
In a circuit consisting of three branches that are respectively ab , 
ad , cb , cd ’ and db, let r, r Y , and r 2 , be the respective resistance of 
the several branches as indicated in the diagram, and i, i lf and i 2f 


z, 



E 


z 


the corresponding currents. Let E x and E 2 be the acting E.M.Fs, 
then the applications of Kirchhoffs laws give rise to the following 
equations for the current values : — 


i — ^i r 2 4= E 2 ri > 
rr i + rr 2 + r x r 2 ’ 

ix = ( r + ? 2) T' E 2 r ' 
rr x + rr 2 + r x r 2 

__ ^-2 + *2) T ^ 

rr x + rr 2 + r x r 2 


(115) 

(116) 
(117) 


When the double sign (4= or T) is used, the upper sign is to be taken 
in cases where the E.M.Fs oppose each other, and the lower one 
where the E.M.F.s act together. Considering these equations, it is 
evident that, excepting when particular values are assigned to 












CONTINUOUS CURRENT CONDUCTORS. 


285 


the constants of* the circuits, there will be current in all of the 
branches. 


To make i~ 0 , — 

E\ _ r x 
E 2 r 2 ’ 

To make ^ = 0, — 

E x _ r 

E 2 r -)- r 2 


To make i 2 = 0, — 



r + r x 
r 


or E x — E 2 . 


or E x 



r 

r + r 2 ' 


or E x 



r + r x 
r 


(118) 


(119) 


( 120 ) 


As there are several quantities ( E.M.F.s and resistances) in these 
expressions, parallel results may be attained by changing either one, 



Fig. 205. 


or any desired combination, of the variables to attain the desired 
ratios. When there are u branches in the network and n E.M.F.s 
acting, similar equations may be deduced. 

355. Case 4. — The last elementary combination is illustrated 
in Fig. 205, and consists of an E.M.F. acting in a circuit of seven 
branches, ab, ad , be , be, dc, de, and ec as shown. As above, let E 
represent the E.M.F ., i, t \, etc., and r, r x , etc., the respective currents 
and resistances in the several branches as shown in the diagram, 
then, — 


i _ r \ r 2 + r \ r \ T + r z r A + r % r h + r 4 r 5 ^ ^ ^0^ 


k) 


h 


__ r 2 r 3 4- r 8 r 4 + r 3 r 5 + r 4 r 5 x 
N 


( 122 ) 














286 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


i) 

r x 7\ + r 3 r 4 + r ? r r> + r 4 r 5 

X E\ 

(123) 

N 

m) 

r x r 2 + r x r 4 + r x r 5 + r 2 r 5 

X E ; 

(124) 

4 " ~ N ~ 

7l) 

r \ r i + r x r 6 + r 2 r 3 + r 2 r 3 

X E ; 

(125) 

?4 “ N 

°) 

• r \ r \ r 2 r 3 v- J7 

h- N x-z. 


(126) 


In the above expressions, — 

N = rr x )\ + rr x r 4 -f rr x r B + rr Nz + rr 2 r 3 -f rr 3 r 4 + rr s r 5 + rr 4 r 5 + r x r 2 r 3 
+ r x r 2 r 4 + r x r z r 4 -f- r x r 3 r 3 + /yv's + r 2 r 3 r 4 + r 2 r 3 r 5 + r 2 r 4 r 6 . 

Equation (126) shows that in the branch ec, the current i s becomes 
zero, when, — 

7 '\ 7‘ 3 ? i ? 2 /I OT\ 

r x r 4 = r 2 r 3 , or -±- = -5- , or -i = — . (12 <) 

r 2 7 \ r 3 r 4 

356. All networks, no matter how complicated, may be analyzed 
by resolving them into combinations of the foregoing elementary 
forms. By then successively applying the equations given for each 
of the elementary forms and summing the results, the distribution 
of current and potential, no matter how complicated, may be finally 
arrived at. It should be noted, however, that algebraic processes 
of this kind are exceedingly complicated, and are particularly liable 
to lead to error, owing to the multiplicity and complexity of the 
symbols, and, therefore, great care must be taken to avoid numerical 
mistakes in attaining the final result. 







CONTINUOUS CURRENT CONDUCTORS. 


287 


CHAPTER VII. 

CONTINUOUS CURRENT CONDUCTORS. (Continued.) 

PART II.—THE HEATING OF CONDUCTORS. 


Art. 357. Joule’s Law. — A portion of the electrical energy de¬ 
livered to any conductor is found to be expended in the conductor 
itself, and by some mysterious process, sometimes termed by investi¬ 
gators “molecular friction,” is transformed into heat, and serves to 
raise the temperature of the material forming the conductor. Ex¬ 
periment has shown that the quantity of heat thus produced is 
proportional to the square of the current, the resistance of the cir¬ 
cuit, and the time during which the current flows. 

To Doctor Joule is due the mathematical expression for the 
amount of heat thus developed. 

Let I be the current in amperes, 

R the resistance of the circuit, 

T the time in seconds during which the current flows, 

H the heat developed in calories (gramme degree), 
the cross-section of the conductor, 
d the diameter of the conductor, 

/ its length, 

p the specific resistance of the material forming the con¬ 
ductor. 

Joule’s Law indicates, for the amount of heat developed in any 
circuit, — h — 94 i*r t. (128) 

The resistance R of the circuit is pl/s, which, for a cylindrical con¬ 
ductor, becomes Substituting in the preceding formula, — 

(129) 


rr .30557 plPT 

ii - T • 

d 1 


If / and T are written as units of length and time respectively, 
then the above expression, formula (129) gives the amount of heat 
evolved per unit of length of the conductor per unit of time. The 





288 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


heat thus generated augments the temperature of the conductor; and 
were it not for radiation and convection, this elevation of the con¬ 
ductor temperature would increase until the fusing-point of the 
circuit was reached, and the current interrupted by the melting of 
the conductor. When the cooling of the circuit equals the heat 
evolution, equilibrium is obtained, the conductor remaining at a con¬ 
stant temperature above its surroundings, as long as the current 
remains constant. To safely design electrical circuits, in order that 
their carrying capacity may be, on the one hand, such as to exempt 
them from becoming sources of danger, and on the other hand, to 
attain an economical disposition of the conducting material, is a 
matter of supreme importance. 

358. Location of Circuit. — It is necessary to consider con¬ 
ductors under the various aspects in which electrical circuits may 
be placed. 

First. Bare wires may be freely suspended in the atmosphere. 

Second. Bare wires may be inclosed in panel moldings, or 
other forms of interior conduit. 

Third. Insulated wires may be freely suspended in the air. 

Fourth. Insulated cables may be buried in underground con¬ 
duits, or extended under water ; and, as a corollary, adjacent under¬ 
ground conductors may exercise a mutual influence on each other, 
the passage of the current in one cable being sufficient to cause the 
temperature of the conductor to seriously influence that of a neigh¬ 
boring cable. Each of these cases will be considered successively. 

359. First, Bare Wires Freely Suspended. — The resulting 
temperature to be attained by electrical conductors has been studied 
in England by Professor Forbes, and investigated in this country by 
Mr. A. E. Kennedy. Both of these investigators have based their 
researches upon the laws for radiation and convection established by 
Dulong and Petit. Mr. Kennedy’s experiments have been the more 
complete and exhaustive, and, forming a classic paper presented to 
the Edison Convention in 1889, are usually assumed as indicating 
the best present knowledge on the subject. 

360. Radiation and Convection. — Two causes are, manifestly, 
operative to reduce the temperature of a conductor. 

First. Heat may be lost by direct radiation from the surface of 
the conductor. 


CONTINUOUS CURRENT CONDUCTORS. 


289 


Second. Heat may be lost by convection. 

The quantity of heat radiated by a conductor is proportional to 
the amount of radiating surface, the difference in the temperature 
between the conductor and that of its surroundings, the time during 
which radiation takes place, and to an arbitrary coefficient depending 
upon the nature of the radiating surface. 

Thus, if k be the coefficient of radiation per unit of area, 

0 the temperature of the surrounding air, 
t the temperature attained by the conductor, 
the radiating power of length / and diameter d is ki rdl(t — 0) T. 

If / and T are respectively units of length and time, the expres¬ 
sion per unit of length per unit of time becomes 3.1416 Kd(t-O). 

Mr. Kennedy’s experiments, confirming the investigations of 
Dulong and Petit, indicate that for radiation the quantity of heat 
dissipated per square centimeter of surface is given by the expres¬ 
sion (1.OO77 0 ) (1.007'-l) C, in which C is a constant depending upon 
the physical character of the radiating surface. 

361. For highly polished metals (the poorest radiators), C is 
equal to one; while for roughened and blackened surfaces C has a 
greater value, being usually assumed as two, but sometimes rising to 
a higher value. For electrical calculation, it is more convenient 
to express the energy lost in the conductor in watts, instead of 
thermal units or calories. 

Denoting then the total energy transformed in the conductor 
into heat by W watts, and that portion of IF lost by radiation by 
W r , and the portion lost by convection by W c , — 

IF = IV r + IV c . 

Under these circumstances, the expression for the radiation per 
square centimeter is — 

\V r = .05625 (1.00770) (1.007' - 1) C. (130) 

For a polished wire of diameter d and any surface, the radiation 
becomes— ^ = .05625 [(1.0077#) (1.007' — 1) WC] (131) 

per unit of length and time. 

362. Cooling is also aided by convection. The amount of heat 
lost from this cause, as determined by Mr. Kennedy, is — 

IV C = .00175 (/ - 0); 


(132) 




290 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


and the investigation indicated that this relation was independent of 
the amount of surface, holding true for a wire of any diameter per 
unit of length. 

This relation is found strictly applicable for still air in an 

inclosed location. But Mr. Ken nelly’s experiments show that, for 

ordinary aerial lines, even under the most unfavorable assumption 

of calm weather, the above quantity can be increased by an amount 

equal to— . . 

1 .013 d (t — 0). 

Therefore the complete expression for W c becomes — 


W c = (.00175 + .013 d) (t — 0). (133) 

363. The amount of energy in watts W developed in the con¬ 
ductors, per unit of length and time, is PR. As soon as the tem¬ 
perature of the conductor ceases to rise, there must evidently be 
equilibrium between the heat evolution in the conductor and the 
amount lost by radiation and convection. Then, — 


PR = .05625 [(1 .OO77 0 ) (1.007' — 1)] Cird + [(.00175 + .013 d) (/ - 0)]. 

To simplify, let [(.00175 -f- .013 d) (t — 0)] = a, ^ ^ 

and .05625 tt [(1.00770) (1.007' - 1)] = b ; 

then, PR — bdC + a ; 


but 



at any temperature above 0° C. ; hence, as the temperature attained 
by the conductor is a function of the resistance, this quantity must 
be substituted for R. 


7rd 2 (bdC T <?) _ 7 7v/ 2 ^ bdC -f- a 

4 Po (1 + a/ + fit 2 ) 4 p 0 (1 -f- at -f- fit 2 ) 


/ 


= .8862 d 1/-- 

V Po (1 


bdC -f- a 


+ a t fit' 2 ) 


(13 5) 


As both 0 and t enter into the quantity under the radical sign, / can 
only be obtained by successive approximations. 

364. In Tables Nos. 22 and 23 will be found the values of — 


Rt — Po (1 + + Z^)? 

.05625 tt (1.00770), 
1.007' - 1, 

0.00175 + 0.013 d\ 


and 









CONTINUOUS CURRENT CONDUCTORS. 


291 


by means of which, by simple substitution, the carrying capacity of 
any wire in amperes may be found for any surrounding temperature, 
and any determined rise of temperature, between 0° and 200° C. 


Table No. 22. 

Copper Resistance. 



365. In Table No. 22 the base line is assumed horizontally op¬ 
posite 1 on the left-hand vertical axis, the relative resistances being 





































































































































































292 THE ELECTRICAL TRANSMISSION OE ENERGY. 

reckoned positively upward, and the relative conductivity negatively 
downward. The specific resistance is a positive curve, running up¬ 
ward from the point 1.589 on the left-hand axis. The temperature 


Table No. 23. 



scale will be found horizontally along the bottom, and the resistance 
scale on the left hand. In Table No. 23, for the curve giving values 
of .00175-f.013</, the values of d are horizontally along the top of the 







































































































































CONTINUOUS CURRENT COA T DUCTORS. 


293 


sheet, the temperature scale horizontally along the bottom. Two 
curves are given for this expression ; one plotted to the natural scale 
of the sheet, as indicated on the left-hand axis, and the other exagger- 


Table No. 25. 



ated ten times, the axis being on the right hand. The other two 
curves, for values of .05625^ (1.0077 9 ) and 1.007* —1, hardly need 
explanation, being referred to the lower and left-hand axes. 

366. By means of the preceding formulae and tables, quite accu- 














































































































































































































































































































































































































































































































































































































294 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


rate determinations may be made of the probable temperature to be 
obtained in any conductor by the passage of any current. For aerial 
lines, the free circulation of air and effect of wind is usually to reduce 
the temperature below that indicated by the formula. For a good 
approximation, the Tables Nos. 24 and 25, deduced from Kennedy’s 
experiments, may be employed for determining the probable temper¬ 
ature of the conductors. 


Table No. 26. 

Safe Currents for Paneled Wires. 


Amperes. 

Minimum Safe 
Diameter of 
Copper Wire. 

Circular Mils 
per Ampere. 

Fall of Poten¬ 
tial in Wire 
at Full Load. 

Amperes. 

Minimum Safe 
Diameter of 
Copper Wire. 

Circular Mils 

per Ampere. 

Fall of Poten¬ 
tial in Wire 
at Full Load. 

Inches. 

Cms. 

Volts 

per 

Foot. 

Volts 

per 

Meter. 

Inches. 

Cms. 

Volts 

per 

Foot. 

Volts 

per 

Meter. 

1 

0.015 

0.038 

225 

0.0503 

0.165 

130 

0.377 

0.958 

1090 

0.0103 

0.0337 

5 

0.043 

0.109 

370 

0.0305 

0.100 

140 

0.396 

1.01 

1120 

0.0099 

0.0327 

10 

0.069 

0.175 

480 

0.0237 

0.0777 

150 

0.415 

1.05 

1150 

0.00975 

0.0320 

15 

0.090 

0.229 

540 

0.0208 

0.0681 

175 

0.461 

1.17 

1210 

0.00929 

0.0305 

20 

0.109 

0.277 

590 

0.0189 

0.0621 

200 

0.504 

1.28 

1270 

0.00887 

0.0291 

25 

0.126 

0.320 

640 

0.0177 

0.0581 

225 

0.545 

1.38 

1320 

0.00853 

0.0280 

30 

0.142 

0.361 

670 

0.0167 

0.0548 

250 

0.585 

1.49 

1370 

0.00817 

0.0268 

35 

0.158 

0.401 

710 

0.0158 

0.0518 

275 

0.623 

1.58 

1410 

0.00793 

0.0262 

40 

0.172 

0.437 

740 

0.0152 

0.0499 

300 

0.660 

1.68 

1450 

0.00771 

0.0253 

45 

0.186 

0.472 

770 

0.0147 

0.0481 

325 

0.697 

1.77 

1490 

0.00753 

0.0247 

50 

0.200 

0.508 

800 

0.0141 

0.0461 

350 

0.732 

1.86 

1530 

0.00734 

0.0241 

55 

0.213 

0.541 

825 

0.0136 

0.0447 

375 

0.766 

1.95 

1570 

0.00716 

0.0235 

60 

0.225 

0.572 

845 

0.0133 

0.0437 

400 

0.800 

2.03 

1600 

0.00714 

0.0231 

65 

0.238 

0.605 

870 

0.0129 

0.0423 

425 

0.832 

2.11 

1630 

0.00692 

0.0227 

70 

0.250 

0.635 

890 

0.0126 

0.0413 

450 

0.865 

2.20 

1660 

0.00674 

0.0221 

75 

0.262 

0.655 

915 

0.0123 

0.0403 

475 

0.897 

2.28 

1690 

0.00665 

0.0218 

80 

0.274 

0.696 

940 

0.0120 

0.0393 

500 

0.928 

2.36 

1720 

0.00652 

0.0214 

85 

0.2 S 5 

0.724 

960 

0.0118 

0.0386 

550 

0.9 S 8 

2.51 

1775 

0.00634 

0.0208 

90 

0.296 

0.752 

970 

0.0116 

0.0379 

600 

1.049 

2.66 

1840 

0.00616 

0.0202 

95 

0.307 

0.780 

990 

0.0113 

0.0372 

700 

1.16 

2.95 

1920 

0.00585 

0.0192 

100 

0.318 

0.808 

1010 

0.0111 

0.0365 

800 

1.27 

3.23 

2020 

0.00558 

0.0133 

110 

0.339 

0.861 

1040 

0.0108 

0.0353 

900 

1.37 

3.48 

2080 

0.00539 

0.0177 

120 

0.358 

0.909 

1070 

0.0105 

0.0346 

1000 

1.47 

3.73 

2160 

0.00521 

0.0171 


Data. — Insulated house wires carrying continuous currents, and incased in wooden paneling. Copper 
resistivity, 1.650 microhms @ 0° C . = 1.870 microhms @ 31° C . assumed temperature of full load; conduc ¬ 
tivity allowed, 98 per cent. 


367. It should be carefully noted that the rise of temperature of 
the conductor increases its resistance a very notable amount, and 
should not be forgotten in the design of the circuit. To compensate 
for this extra resistance, either additional conductor section must be 
provided, or a greater pressure at the terminals of the generator. 
See Table No. 26 for full data for proportioning circuits. 



































CONTINUOUS CURRENT CONDUCTORS . 


29 5 


368. Second, Paneled Wire. — Interior wiring is usually either 
protected by ornamental moldings, or run in interior conduits of some 
description. Being thus in a confined location, the effects of radia¬ 
tion and convection are reduced to a minimum. The circuits may 
also be surrounded by inflammable material, so that particular care 
must be exercised to secure safety. The consensus of opinion of the 
American and Foreign Underwriters’ Associations limits the allowed 
elevation of temperature in paneled conductors to a rise not to exceed 
10° C. For this amount, Mr. Kennedy's experiments indicate the 
safe current in amperes to be expressed by the relations, — 

/== 560//§.if d is in inches. 

I = 0.01775//§.if is in mils. 

/ = 138 //2 .if // is in centimeters. 

1 = 4.375//£ if d is in millimeters. 

Reciprocally — 

d = 0.0147/S.if d is in inches. 

d = 14.7/s.if // is in mils. 

d— 0.0374/S.if d is in centimeters. 

d= 0.374/S.if // is in millimeters. 

From these data, and as a result of his experiments, Mr. Ken¬ 
nedy gives Tables Nos. 26 and 27; Table No. 27 indicating the cur¬ 
rent and resulting temperature, in paneled wire, up to 300 amperes, 
and to a diameter of .450"; Table No. 26 giving the minimum safe 
diameter and fad of potential, up to 1,000 amperes, for a rise of tem¬ 
perature of 10° C. 

369. Third, Insulated Wire Freely Suspended. — Apparently, 
insulated wires, with their non-conducting coatings, would be sub¬ 
jected to a greater elevation of temperature than bare wire. The 
insulation, however, increases the amount of radiating surface of the 
conductor, and also provides a surface which, from its physical char¬ 
acteristics, is a much more efficient radiator than the polished metal. 
It seems probable that this increased efficiency and size of the sur¬ 
face fully counterpoise, at least in most cases, the non-conducting 
effect of the insulating covering. From Professor Forbes’s experi¬ 
ments, this relation would seem to be substantiated, and therefore 
ordinary insulated wires may usually be treated as if they were unin¬ 
sulated. This branch of the subject, however, is worthy of more 
extended investigation. 











296 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


370. Rheostats and Heaters. — In many electrical appliances 
it is customary to control the amount of energy delivered to the trans¬ 
lating device by the aid of a resistance capable of being varied to suit 


Table No. 27. 



the demands upon the receiver, which acts as a dam, or valve, inter¬ 
posed in the circuit to control the amount of current. Such resist¬ 
ances are termed rheostats, and dissipate a certain amount of energy 
as electricity, transforming same into heat. The determination of 








































































































































































































CONTINUOUS CURRENT CONDUCTORS. 


297 


the size of wire to be used for such purposes may be made by the use 
of the preceding formulae. Usually, however, rheostats are made 
either of German silver or iron wire; and for either of these materi¬ 
als, Tables Nos. 28, 29, and 30 may be used to obviate calculation. 
A number of devices have recently made their appearance for heating 
by electricity, such as car-heaters, flat-irons, cooking-utensils, and the 
like. Nearly all of them are based upon the transformation of elec¬ 
trical energy into heat energy by the interposition of the resistance 
of a bare conductor, usually consisting of a small metallic wire em¬ 
bedded in a vitreous enamel of high melting-point. 

Table No. 28. 


Safe Current for Galvanized Iron Wire. Rheostats. 


D in Circular 
Mils. 

Maximum Saff. 
Current in 
Amperes in 
Wood Frames. 

Maximum Safe 
Current in 
Amperes in 
Iron Frames. 

Maximum Safe 
Current for 
One Minute. 

Feet per 
Ohm. 

59536 

55 

63.8 

125 

645 

50625 

48 

55.6 

110 

549 

42849 

41 

47.5 

90 

463 

36864 

30 

34.8 

78 

398 

31329 

26 

30.1 

67 

337 

26244 

23 

26.6 

56 

283 

21904 

20 

23.2 

46 

236 

18225 

17 

19.7 

36 

196 

14400 

14.5 

16.2 

32 

155 

11025 

12 

13.9 

22 

119 

8464 

10 

11.6 

17 

91.4 

6400 

8 

9.28 

13 

69.1 

5184 

6 

6.96 

11 

56.0 

3969 

5 

5.8 

8.9 

42.8 

2916 

3.7 

4.29 

8 

31.4 


The energy supplied by the device is, by the resistance of the 
wire, transformed into heat, and serves to raise the temperature of 
the entire apparatus to a useful limit. All such devices may be cal¬ 
culated by the methods already indicated, due consideration being 
given to the conducting power of the enamel, in which the heating 
part of the circuit is embedded. Some heating contrivances, how¬ 
ever, designed to operate upon alternating current circuits, take 
advantage of the work done by hysteresis in rapidly alternating mag¬ 
netic cycles. For devices of this kind, it is hardly necessary to state 
that the preceding calculations do not apply. 

371. Cost of Electrical Heating. — The cost of electrical heating 
in its various forms is, probably, the most important factor in the 














298 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


development of this branch of industry. Probably electrical heating 
has its widest development in the warming of street-cars during the 
cold season of the year. Car-heaters operated by coal cost from 
115.00 to $25.00, with an installation expense of $1.50. With fuel 
at $4.50 per ton, and labor $1.50 per day, the cost of operating coal 
car-heaters is about 16 cents per day of 24 hours. Per contra, elec¬ 
tric heaters cost from $35.00 to $40.00, and the expense for current 
amounts to from 30 to 40 cents per day in moderate weather, and 
from 60 to 80 cents per day in the coldest weather. These figures 
are based on fuel at $3.00 per ton at the generating-station. P'or 


Table No. 29. 

Safe Current for Tinned Iron Wire. Rheostats. 


D in Circular 
Mils. 

Maximum Safe 
Current 
Capacity. 
Wood Frame. 

Maximum Safe 
Current 
Capacity. 

Iron Frame. 

Maximum Safe 
Current 
Capacity for 
One Minute. 

Feet per 

Ohm. 

16509 

17.4 

20.3 

43.6 

205 

13094 

14.6 

17.1 

36.6 

173 

10381 

12.3 

14.3 

30.8 

137 

8234 

10.3 

12 

25.7 

108 

6529 

8.7 

10.1 

21.8 

86.4 

5178 

7.3 

8.5 

18.3 

68.5 

4106 

6.1 

7.1 

15.3 

54.3 

3256 

5.1 

6 

12.9 

43.1 

2582 

4.3 

5 

10.8 

34.1 

2048 

3.6 

4.2 

9.1 

27.1 

1624 

3.0 

3.5 

7.6 

21.4 

1252 

2.52 

2.9 

6.3 

16.5 

1021 

2.17 

2.5 

5.4 

13.5 

810 

1.82 

2.1 

4.5 

10.7 

642 

1.53 

1.77 

3.8 

8.49 

509 

1.28 

1.49 

3.2 

6.73 

404 

1.08 

1.2 

2.3 

5.34 


cooking by electricity, it is found that an ordinary oven requires 
about 25 amperes at 110 volts, a frying-pan 2 \ amperes, a flat-iron 
from 2 to 3 amperes, and a soldering-iron from 2 to 3 amperes. It 
is claimed that ordinary meat can be roasted in an electric oven, sup¬ 
plied with 25 amperes, in from 7 to 8 minutes per pound of meat 
introduced. For heating water, the cost under the present rates for 
current, averages about 2 to 5 cents per gallon of water heated. An 
ordinary oven is entailed with an expense of from 3 to 6 cents per 
hour. Under these circumstances, if the electrical current be esti¬ 
mated at an expense of $60.00 per H.P. annum of 400 hours, it 












CONTINUOUS CURRENT CONDUCTORS . 


290 


would correspond to coal at $6.00 a ton, which is not very different 
from the actual expense to small consumers. 

372. Fuse Wires. — Electrical circuits are protected against 
overloading, in the majority of cases, by the interposition at various 
points of short pieces of fusible metal so designed that a slight 
access of current above the normal amount, for which the circuit is 


Table No. 30. 

Safe Current in German Silver Wire. Rheostats. 


D IN 

Circular 

Mils. 

Maximum Safe 
Current in 
Amperes. 

Feet per 
Ohm. 

D IN 
Circular 
Mils. 

Maximum Safe 
Current in 
Amperes. 

Feet per 
Ohm. 

10381 

8.5 

60.9 

1252.4 

1.21 

7.25 

8234 

5.4 

47.6 

1021.5 

.99 

5.91 

6529.9 

4.6 

37.8 

810.1 

.88 

4.69 

5178.4 

3.8 

29.9 

642.7 

.66 

3.72 

4106.8 

3.2 

23.7 

509.45 

.55 

2.95 

3256.7 

2.7 

18.8 

404.01 

.488 

2.33 

2582.9 

2.3 

14.9 

320.04 

.434 

1.85 

2048.2 

1.9 

11.8 

254.01 

.385 

1.47 

1624.3 

1.65 

9.40 

201.5 

.343 

1.16 


calculated, will melt the fuse, and afford protection from further in¬ 
jury by opening the leads. The first experimental determination of 
the constants for fuse wires was made by Mr. Preece in 1884 ; the 
investigation showed that the relation between the diameter of the 
wire and the fusing current is expressed by the equation, — 

I = ad § , (136) 

in which a is a constant for a given metal or alloy. In 1890 con¬ 
tinued investigation by Mr. Preece (published in the Electrical Eji- 
gineer) showed that the following values for a should be assumed : — 


Table 

Copper. 2530 

Silver.1900 

Aluminum.1873 

Platinum.1277 

German Silver. . . . 1292 


No. 31. 


Platinoid.1173 

Iron. 777.4 

Tin. 405.5 

Alloy (Tin 1, Lead 2) . 325.5 

Lead. 340.6 


These values indicate the current in amperes required for fusing 
a cylindrical conductor of one centimeter in diameter, of each of the 
materials named. Still more recent data by the same author are com- 





















300 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Table No. 32. 

Giving the Sizes of Various Wires which will be Fused by a Given Current. 

By Mr. W. H. Preece. 


Current 

in 

Amperes. 

Tin Wire. 

Lead Wire. 

Copper 

Wire. 

Iron Wire. 

Diameter 

Inches. 

Approx. 
S. W. G. 

Diameter 

Inches. 

Approx. 
S. W. G. 

Diameter 

Inches. 

Approx. 
S. W. G. 

Diameter 

Inches. 

Approx. 

S. W. G. 

1 

0.0072 

36 

0.0081 

35 

0.0021 

47 

0.0047 

40 

2 

0.0113 

31 

0.0128 

30 

0.0034 

43 

0.0074 

36 

3 

0.0140 

28 

0.0168 

27 

0.0044 

41 

0.0097 

33 

4 

0.0181 

26 

0.0203 

25 

0.0053 

39 

0.0117 

31 

5 

0.0210 

25 

0.0236 

23 

0.0062 

38 

0.0136 

29 

10 

0.0334 

21 

0.0375 

20 

0.0098 

33 

0.0216 

24 

15 

0.0437 

19 

0.0491 

18 

0.0129 

30 

0.0283 

22 

20 

0.0529 

17 

0.0595 

17 

0.0156 

28 

0.0343 

20.5 

25 ’ 

0.0014 

16 

0.0690 

15 

0.0181 

26 

0.0398 

19 

30 

0.0094 

15 

0.0779 

14 

0.0205 

25 

0.0450 

18.5 

35 

0.0709 

14.5 

0.0864 

13.5 

0.0227 

24 

0.0498 

18 

40 

0.0840 

13.5 

0.0944 

13 

0.0248 

23 

0.0545 

17 

45 

0.0909 

13 

0.1021 

12 

0.0268 

22 

0.0589 

16.5 

50 

0.0975 

12.5 

0.1095 

11.5 

0.0288 

22 

0.0632 

16 

60 

0.1101 

11 

0.1237 

10 

0.0325 

21 

0.0714 

15 

70 

0.1220 

10 

0.1371 

9.5 

0.0360 

20 

0.0791 

14 

80 

0.1334 

9.5 

0.1499 

8.5 

0.0394 

19 

0.0864 

13.5 

90 

0.1443 

9 

0.1621 

8 

0.0426 

18.5 

0.0935 

13 

100 

0.1548 

8.5 

0.1739 

7 

0.0457 

18 

0.1003 

12 

120 

0.1748 

7 

0.1964 

6 

0.0516 

17.5 

0.1133 

11 

140 

0.1937 

6 

0.2176 

5 

0.0572 

17 

0.1255 

10 

160 

0.2118 

5 

0.2379 

4 

0.0625 

16 

0.1372 

9.5 

180 

0.2291 

4 

0.2573 

3 

0.0676 

16 

0.1484 

9 

200 

0.2457 

3.5 

0.2760 

2 

0.0725 

15 

0.1592 

8 

250 

0.2851 

1.5 

0.3203 

0 

0.0841 

13.5 

0.1848 

6.5 


Table No. 33. 


Data Commercial Fuse Wire. 


l Rated Capacity. 
Amperes. 

Fusing Current. 
Amperes. 

Diameter in Thou¬ 
sandths of an 
Inch. 

Sectional Area of 
Wire. Fractional 
Parts of Square 
Inch. 

B. and S. Gauge. 
Nearest Number. 

Rated Capacity. 
Amperes. 

Fusing Current. 
Amperes. 

Diameter in Thou¬ 
sandths of an 
Inch. 

Sectional Area of 
Wire. Fractional 
Parts of Square 
Inch. 

B. and S. Gauge. 
Nearest Number. 

1 

1.730 

.010 

.00007 

30 

40 

54.10 

.100 

.00785 

10 

3 

4.892 

.020 

.00031 

24 

50 

63.11 

.110 

.00950 

9 

5 

8.988 

.030 

.00070 

20 

60 

81.08 

.130 

.01327 

8 

7 

11.32 

.035 

.00096 

19 

70 

90.61 

.140 

.01539 

7 

10 

13.84 

.040 

.00125 

18 

80 

100.50 

.150 

.01767 

64 

15 

19.34 

.050 

.00196 

16 

90 

110.70 

.160 

.02010 

6 

20 

25.42 

.060 

.00294 

14 

100 

132.10 

.180 

.02544 

5 

25 

32.04 

.070 

.00384 

13 

125 

154.70 

200 

.03141 

4 

30 ' 

39.14 

.080 

.00502 

12 


























































SECTION IN SQUARE MILS. 


CONTINUOUS CURRENT CONDUCTORS . 


301 


Table No. 34. 






































802 


THE ELECTRICAL TRANSMISSION OF ENERGY,\ 


piled in Table No. 32. The more fusible metals, such as lead, tin, or 
bismuth, or alloys of various proportions of them, are chiefly used for 
fuse wires ; and great difficulty has been experienced in obtaining 

Table No. 35. 



veritable ratings. As each manufacturer used different proportions 
of the alloying ingredients, designating them simply by trade num¬ 
bers, and as usually different batches from the same maker possess 





































CONTINUOUS CURRENT CONDUCTORS . 


303 


varying melting-points, owing to differences in composition, no rules 
could be given for fuse wires, beyond the arbitrary directions of the 
maker. Mr. Bathurst, in the Electiical World , has given the results 
of a recent investigation of the subject, deducing the results given in 
Tables Nos. 33, 34, and 35. 

373. The terminals to which the fuse is connected exercise a 
very marked effect upon the fusing-point, especially when the fuse is 
of short length. Some experiments made by Mr. C. P. Matthews of 
Cornell University indicate the relation which exists between the 
length of a fuse and the amount of current required to melt it. 


Table No. 36. 

Relation between Length and Carrying Capacity of ITuse Wires. 



These relations are plotted in Table No. 36. For the curve A in 
this table the axis of X indicates the length of the fuse between 
terminals, while the axis of Y gives the fusing current in amperes 
for each length. For example, it will be noted that a fuse eight 
inches in length requires a current of 6.6 amperes, while a half-inch 
fuse of the same material, tin, carries a current of 12.5 amperes ; 
thus showing a variation of more than 100 per cent in the carrying 
capacity of the fuse, produced simply by the effect of its length. 
The terminals act to conduct away the heat developed in the fuse by 
the passage of the current, and to dissipate the same, so that the 
heat energy developed is not allowed to act upon the safety device. 






































304 


THE ELECTRICAL TRANSMISSION OF ENERGY . 


The curves B and C in Table No. 36 indicate the effect of inclosing 
the fuse wire in a glass tube, in order to concentrate the heat action. 
The inclosure acts to check radiation and convection, and so 
depresses the carrying capacity, causing the fuse to fail with a 
smaller current. Manifestly, fuses should be selected with reference 
to the kind of fuse block in which they are to be used, as a closed 
block would evidently require a larger fuse than one freely exposed 
to the atmosphere. 

The effect of time during which the current acts, also exercises 
an important factor in the behavior of fuse wires. Table No. 37 

Table No. 37. 

Effect on Carrying Capacity of Fuse Wires of the Duration of the Current. 

50 
45 
40 

35 

l- 

5 30 
cc 
cc 

3 OK 
O ~ D 

o 

? 20 
w 
3 

15 
10 

5 

0 

1 

DIAMETER IN MILS. 



indicates the importance of this factor. Curve A' indicates the 
behavior of a fuse under a current causing failure in twenty seconds, 
B' under a current causing failure in ten seconds, while curve C 7 
is the rating of the fuse. The results of Mr. Matthews’s experiments 
on tin-lead alloys are embodied in Tables Nos. 38 and 39. The 
tests on the actual compositions given in Table No. 38 indicate that 
the mixture used quite closely followed the formula, — I = ad*, from 
which, for the alloys given, the breaking current for various sizes of 
wire may be found. The fusing constant for unit wires of lead-tin 
alloys was determined and plotted in Table No. 39. From this curve, 
the current to fuse any alloy of lead and tin may be ascertained, and 
































CONTINUOUS CURRENT CONDUCTORS . 


305 


by substituting in Formula (136) the limiting current deduced for 
any wire. 

374. It has also been ascertained that the behavior of the fuse 


Table No. 38. 


Carrying Capacity, Lead and Tin Fuse Wires. 



0 16 22 28 34 40 46 52 58 64 70 76 82 88 94 100 

DIAMETERS 


Table No. 39. 

Fuse Wire Curves, Lead and Tin Alloys. 



i 


wires under alternating currents appears to be different from that 
under a continuous current. 

Experience has shown that the action of the alternating current 
seems to have a disintegrating effect upon the fuses, which causes 





















































306 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


- them to blow more readily after use, thus necessitating a con¬ 
stant renewal of the fuses, and supervision over the circuits. From 
investigation by Mr. Sturtevant of Cornell University, it would 
seem that the alternating current exercises an action upon the fuse 
wire, which causes some molecular change, probably making the wire 
crystallize, and causing the fuse to become brittle. As a result of 
this change, the fuses, after a short time, were found to fail with 
a lower current on an alternating circuit than caused them to yield 
when they were first introduced. These experiments indicate a 
grave objection to the use of fuse wires as protectors for alternating 
circuits, from the fact that if when first introduced they have only 
such a reasonable margin of safety as will save the circuit from 
injury from overloading, they will inevitably fail after a short use, 
thus adding largely to maintenance expense, and to the interrup¬ 
tions to the service. On the contrary, if the fuses are introduced 
of sufficient size in the beginning to have a long life, they will 
not protect the circuits from overloading in the early days of 
their introduction. Other investigators question these conclusions, 
and it is probable that additional experiment is needed to settle the 
question. 

375. Fourth, The Heating of Insulated Cables. — Mr. Ken- 
nelley’s 1 investigations, as given in a recent paper to the Association 
of Edison Illuminating Companies, have also extended to the calcula¬ 
tion of the temperature that insulated, sheathed, or armored cables. 
will probably attain when subjected to the passage of a current. The 
simplest case is that of a solid, cylindrical conductor having a radius 
r, surrounded by an insulated covering of radius r', over which a lead 
sheath or armor wire is laid, the whole cable being placed in such 
a location that the sheath is maintained at the constant temperature 
of the surrounding medium, as, for example, in the case of a subma¬ 
rine cable. The temperature attained by the conductor will depend 
upon the amount of energy transformed into heat in the core, and 
on the resistance offered to diffusion of this heat by the surround¬ 
ing envelope of insulating covering. If the insulator had no thermal 
resistance, the heat would evidently be diffused and carried away as 
fast as it was produced. The transference of heat energy taking 
place between any two planes, separated by a uniform medium, is 

1 Paper before the Edison Illuminating Companies, August, 1893. 


CONTINUOUS CURRENT CONDUCTORS. 


307 


' governed by laws similar to those that apply to electrical circuits. 
So the amount of heat passing depends on the difference of thermal 
potential between the planes, the geometrical form of the medium 
separating the planes, the specific thermal resistance of the medium, 
and the time during which the thermal potential acts. If 0 is the 
temperature of the coolest plane, and t that of the warmest one, then 
t — 0 is the thermal potential tending to cause heat energy to pass 
from one to the other, which, for strict accuracy, should be referred 
to the Centigrade scale of the air thermometer. If / be the distance 
between the planes, S' the cross-section of the separating medium, 
and p' the specific thermal resistance, then, — 

p l 

■ H being expressed in gramme calories. If l and T are units of 
length and time, then, — 

and (/-@) = A r 4- ( 137 > 

p s 


The similarity between this formula and that for the current in 
an electrical circuit is evident. In fact, H can be termed the Heat 
current. For a cable having a conducting core of radius r and a 
coating of insulation r\ Mr. Kennedy shows that the resistance to 
the heat current will be — 



.159 p' log e 



(138) 


therefore, the heat current will be — 

t-6 


H = 


- t-6 = H .159 p' log e 


.159 P log e — 


but H = .24 I 2 R, whence, — 


t-6 


1 ' R ( .159 P ' log e r ' 


To simplify, let — 


A — t — 6, and B — .159 p log e — ; 


I 


■Vs 


(139) 


(140) 


then, 


(141) 










THE ELECTRICAL TRANSMISSION OF ENERGY. 



376. From this formula, the carrying capacity of a submarine 
cable may be calculated when the geometrical dimensions, thermal 
resistance, and permissible core temperature are known. Unfortu¬ 
nately, data on specific thermal resistance are very meager; tests on a 
Siemens cable indicated the thermal resistance to be 750 units, while 
tests on cables buried in sandy soil give 50 as a mean for specific 
resistance for the earth. Additional data, so far as can be ascer¬ 
tained, are given, Table No. 40. With due regard to the preserva¬ 
tion of insulation, the core temperature should never be allowed to 
rise over 60° to 65° C. ; and as the temperature of the cable environ¬ 
ment may reach 30° to 35° C., there remains a possible difference in 
temperature of 35° C. 

Table No. 40. 


Giving Specific Thermal Conductivity in C. G. S. Units. 


Name of Substance. 

Specific 

Conductivity. 

Name of Substance. 

Specific 

Conductivity. 

Vulcanized Rubber. . . 

.000098 

Glass. 

.0005 

Beeswax . 

.000087 

Wood. 

.0003 

Felt. 

.000087 

Caoutchouc. 

.00041 

Vulcanite. 

.000083 

Gutta-percha. 

.00048 

Cotton Wool. 

.000043 

Sandy Loam ..... 

.008 

Sawdust. 

.000123 

Bricks and Cement . . . 

.003 

Sand. 

.000131 

India Rubber. 

.0004 

Paraffine. 

.000113 

Sand with Air Spaces . . 

.09 


377. Conduit Cables. — Conduit cables differ from submarine 
cables to the extent that the sheath is not exposed to the cooling of 
a water circulation, and therefore the sheath more nearly approxi¬ 
mates to the core temperature. In other words, the ground or con¬ 
duit interposes an additional thermal resistance to the diffusion of 
heat. Calling the ground thermal resistance B ', — 


H = 


A 

B + B r 


(142) 


The value of B' is given by the formula,— 


B' = .159 p" log e V« 4 — « 2 , (143) 

in which p" is the ground thermal resistance, and n the ratio of the 
depth of the center of the cable below the top of the soil, to the 
radius of the outside of the cable. For a conduit cable, then, for¬ 
mula (141) must include B', and will stand,— 


/ = 



A 

R (B + B')' 


( 144 ) 




























CONTINUOUS CURRENT CONDUCTORS. 


309 


378. The Effect of Adjacent Cables. — When several cables 
occupy adjacent ducts of a conduit, or are buried in the same trench, 
the temperature attained by each will depend in part on the amount 
of heat it receives from its neighbors. Each cable may be regarded 
as a center of radiation, the surrounding soil being imagined as 
divided into a number of cylindrical layers of increasing diameter 
and decreasing temperature. The effect on neighboring cables may 
be ascertained by determining the temperature of the cylinder in 
which the affected cable rests. For this purpose, Mr. Kennedy gives 
the following Table, No. 41, the left-hand column giving the prob¬ 
able temperature to be found in the successive cylindrical layers in 
per cent of the sheath temperature of the cable at the center; while 
the right-hand column indicates the distance in centimeters of the 
layers from the center. 


Table No. 41. 

Temperature Relations of Neighboring Underground Cables. 


Percentage 
of Sheath 
Elevation. 

Horizontal Dis¬ 
tance between 
Axes. Cm. 

Percentage 
of Sheath 
Elevation. 

Horizontal Dis¬ 
tance between 
Axes. Cm. 

Percentage 
of Sheath 
Elevation. 

Horizontal Dis¬ 
tance between 
Axes. Cm. 

95 

3.15 

GO 

14.58 

30 

56.0 

90 

3.93 

55 

18.16 

25 

71.2 

85 

4.88 

50 

22.65 

20 

91.8 

80 

6.07 

45 

28.88 

15 

121.5 

75 

7.55 

40 

35.38 

10 

169.1 

70 

9.40 

35 

44.38 

5 

269.6 

65 

11.71 






379. Suspended. Cables. — There only remains to consider 
heavily insulated sheathed cables suspended in air. Such cases are 
presented by cables that are in part on pole lines, or that are com¬ 
pelled to pass for some distance through a large vault or subway. The 
limiting current for an aerial cable is obtained from the formula, — 



(145) 


in which e is the total heat emission per unit of area of the sheath. 
With due regard to the safety of the cable, the temperature of the 
sheath should not rise more than 20° or 30° above the atmosphere ; for 
that range e may be assumed as sensibly constant, and its value deter- 


















310 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


mined from equations on page 287, and / determined by substitution 
in (145). 

Concentric Cables. — The case of concentric cables, where one 
conductor is entirely surrounded by another, heat being evolved in 
both conductors, may be treated as an aggravated case of “Adjacent 
Cables and calculated accordingly. Large factors of safety should, 
however, be allowed, as many factors enter into the heating problem 
that are as yet not completely determined. 


| 




CONDUCTORS FOR ALTERNATING CURRENTS. 


311 


CHAPTER VIII. 

CONDUCTORS FOR ALTERNATING CURRENTS. 

Art. 380. General Considerations. — When alternating cur¬ 
rent circuits commenced to attain a commercial importance, they 
were proportioned according to Ohm’s formula and Joule’s formula, 
as given in the preceding chapter ; but results experimentally deter¬ 
mined indicated wide departures from these laws. Sometimes the 
current in the conductors was much less than that which would be 
expected from the electro-motive force and resistance of the circuit. 
In other cases, electro-motive forces absorbed by the circuits were 
far in excess of the product of the current and the resistance of the 
conductor ; and the product of the current in amperes, and the elec¬ 
tro-motive force in volts, failed to give the amount of energy in watts. 
Where more than one electro-motive force operated upon a circuit, 
the resulting electro-motive force was sometimes found to be greater 
than the algebraic sum of the electro-motive forces, and in other 
cases to be less. When branch circuits were used, the currents in 
the respective branches did not divide proportionally to the resist¬ 
ance, thus causing the anomaly of the sum of the currents in the 
branch circuits to be sometimes greater than the total current in the 
main circuit, and sometimes less. In other peculiar instances it was 
found that the electro-motive force at the terminals of long lines of 
mains was greater than the impressed electro-motive force given by 
the generator at the beginning of the circuit. It became, therefore, 
essential to more carefully study the distribution of current and 
potential in alternating circuits, in an endeavor to reconcile these 
anomalies with the laws of the conservation of energy. 

381. In the constant current circuit, the office of the generator 
is to produce at one point in the conductor a constant and steady 
elevation of electrical potential. A familiar comparison may be 
made to the case of an air-blower, or fan. The office of the fan is 
to create a certain elevation of air pressure ; and the quantity of the 
resulting current of air depends entirely upon the friction, or resist- 


312 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


ance, of the pipes or ducts through which the air flows. If the pipe 
leading from the fan be entirely closed, the revolution of the fan- 
wheel simply increases the air pressure inside of the fan-casing; and 
as the inclosed air revolves with the moving wheel, little or no 
energy is consumed beyond that required to overcome the friction 
of the bearings, and no current of air is transmitted. By opening 
the air-pipe a current of air is immediately established, the quantity 
of which depends directly upon the resistance of the pipe. The 
energy of this air-current is directly proportional to the product of 
the pressure given by the fan and the quantity of the air flowing; 
and, consequently, the energy absorbed by the fan is in a like man¬ 
ner proportional to the aforementioned product. A dynamo oper¬ 
ating upon an open circuit is occupied only in raising the electrical 
potential between the brushes ; and, as the circuit is open, no energy 
is expended in the circuit, and no energy is absorbed by the dynamo, 
excepting that necessary to overcome the frictional resistances of 
the machine itself. On closing the circuit through a varying resist¬ 
ance, the energy delivered by the generator to the circuit is directly 
proportional to the product of the current and the electro-motive 
force, while the current is inversely proportional to the resistance ; 
also the energy absorbed by the generator is correspondingly pro¬ 
portional to the same quantities. In the continuous current gener¬ 
ator, the electro-motive force produced is a constant and unvarying 
quantity. With the alternating current generator, the electro-motive 
force is a constantly varying quantity, causing the current to vary in 
a like manner, in which variation may be found the origin of the 
previously mentioned anomalies. 

382. Classification. — The apparent discrepancy between the 
distribution of current and potential in an alternating current circuit, 
and the apportionment as indicated by the laws of Ohm and Joule, 
may be conveniently, for investigation, divided into three parts : — 

Case 1. Skin Effect. 

Case 2. Inductance. 

Sec. a. Effect of Inductance. 

Sec. b. Effect of Mutual Inductance. 

Case 3. Capacity. 

These divisions will now be separately treated. 

383. Case 1 : Skin Effect — Current Density. — According to 


CONDUCTORS FOR ALTERNATING CURRENTS. 313 

% 

the latest theories regarding the nature of electricity, it is believed 
that electrical disturbance is due to elastic reactions set up in the 
ether. In dielectric bodies the ether is, as it were, confined and 
prevented from moving. In conductors, on the contrary, the ether 
particles find themselves at liberty, and are more free to move under 
the stresses set up by electrical action. A conductor, therefore, may 
be simply regarded as a hole in the dielectric, through which the 
stresses set up between the ether particles can relieve themselves 
more freely. Assuming the truth of this supposition, it is evident 
that the dielectric, rather than the conductor, is worthy of interest 
and investigation. Thus, in the case of an alternating current, the 
dielectric is stressed first in one direction and then in the other. 
With a continuous current, however, the stress would always be in 
the same direction. In the latter case, the ether particles, finding 
themselves in the neighborhood of a conductor, would, so to speak, 
soak into the wire, and there relieved from the confining action of 
the dielectric, would be enabled to move and adjust themselves to 
the stress imposed by the generator. Evidently some time must be 
required for this action to take place. With an alternating current, 
however, the ether particles are alternately stressed first in one 
direction and then in the other ; and if the reversals occur so fre¬ 
quently as to prevent the ether particles from penetrating the con¬ 
ductor, it is obvious that the interior of the wire will not be subjected 
to electric action, and will be of little or no service as a conductor. 
An analogy to this phenomenon may be obtained in alternately 
heating and cooling a body. Consider a round copper rod (one of 
the best conductors of heat) to be alternately plunged with great 
rapidity first into a furnace and then into a freezing mixture. The 
first effect of the furnace is to heat intensely the exterior of the rod, 
and by conduction all portions of the metal tend to assume the same 
temperature. This, however, requires time ; and if, before the heat 
energy can proceed to the central portion of the rod, it be plunged 
into the freezing mixture, the effect of the furnace is annulled, and 
the conductor tends to become chilled. Thus, it is conceivable that, 
if the alternations be sufficiently rapid in proportion to the speed of 
conduction, the interior of the body could never be affected, no 
matter how intense the source of either heat or cold. So, with an 
alternating current, if the reversals are extremely rapid, the outer 


314 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


layers of the conductor only are affected, and the electrical action 
commonly known as “A Current” is confined to the surface of the 
conductor. If the conductor be large and the reversals quite rapid, 
the exterior only plays a part in the transference of energy. Owing 
to this restriction of the current to the surface of the conductor, it is 
plain that the interior becomes of no value for the purpose of power 
transmission, and that calculations as to the resistance of the circuit 
must be based solely upon that portion of the cross-section that is 
affected at each reversal. Evidently the resistance is increased in 
proportion to the restriction of the conductor, and this in turn is 
proportional to the frequency of the reversals. The extra resistance 
entailed by lack of penetration of the energy into the body of the 
conductor is chiefly noticeable with wires or cables of large size, and 
may readily be practically obviated by using a stranded conductor, in 
which the interior strands are frequently brought to the surface, or 
one formed of strips, in which the various component parts of the 
conductor are brought into close proximity with the dielectric, in 
order that they may be more fully exposed to the penetrating influ¬ 
ence of the energy. This phenomenon of increased resistance has 
been treated from a mathematical standpoint by Lord Kelvin, Lord 
Rayleigh, and Mr. Heaviside ; but the mathematical discussion tran¬ 
scends the scope of this volume. Professor Gray, 1 in his Absolute 
Measurements in Electricity and Magnetism , shows that the effec¬ 
tive resistance to rapidly alternating currents, may, without sensible 
error, be represented by the ohmic resistance of a cylindrical shell of 
certain thickness, on the outside of the conductor, throughout which 
the current density is sensibly constant. The following, Table 
No. 42, gives the thickness of copper and iron shells to be assumed 
in calculating the apparent resistance of alternating circuits : — 

Table No. 42. 

Thickness of Shell on Cylindrical Conductors Affected by the Current in 

an Alternating Circuit. 


Frequency. 

Thickness of 

Shell in Cm. 

Copper. 

Iron. 

80 

.719 

.0976 

120 

.587 

.0789 

160 

.509 

.0691 

200 

.455 

.0671 


1 Absolute Measurements in Electricity and Magnetism , vol. ii., part i., p. 338 . 









CONDUCTORS FOR ALTERNATING CURRENTS. 


315 


A consideration of these data indicates the futility of employing 
thick wire or cable for high frequency currents, as the center of the 
conductor is valueless. Lord Kelvin shows that the increase in 
apparent resistance due to unequal current density, for the same 
wires, varies as the square root of the frequency, that is as V;/, and 
gives the following, Table No. 43, showing the factor for virtual or 
effective resistance for periods of 40 and 80, and for wires from 5 
cm. to 10 cm. in diameter : — 


Table No. 43. 

Factor for Virtual Resistance in Alternating Current Circuits. 


Factor for 
Virtual 
Resistance. 

Diameter in 

Centimeters. 

Factor for 
Virtual 
Resistance. 

Diameter in 

Centimeters. 

Frequency 80. 

Frequency 40. 

Frequency 80. 

Frequency 40. 

1.0000 

0.5 

0.71 

1.863 

4.5 

6.36 

1.0001 

1.0 

1.41 

2.043 

5.0 

7.07 

1.0258 

1.5 

2.12 

2.220 

5.5 

7.78 

1.0805 

2.0 

2.83 

2.394 

6.0 

8.48 

1.175 

2.5 

3.54 

3.096 

• . • 

11.3 

1.319 

3.0 

4.24 

3.794 

10 

14.1 

1.492 

3.5 

4.95 

5.573 

15 

21.2 

1.678 

4.0 

5.66 

7.325 

20 

28.3 


To use this Table, find in the column headed “Diameter” the 
size of the conductor ; opposite, in the column headed “ Factor,” will 
be found a quantity by which the ohmic resistance is to be multiplied 
to obtain the virtual resistance. For any other frequency, multiply 
the factor by the V;/. 

384. Case 2 : Inductance. 

Sec. a. — Effect of Inductance. 

Magnetic Field Due to Current. — If some iron filings be sprinkled 
on a glass plate placed over a small magnet, and the plate gently 
tapped to overcome the frictional resistance between the surface and 
the filings, the particles of iron are seen to arrange themselves along 
a series of lines that form closed curves extending from pole to pole 
of the magnet. 

385. To Faraday is due the conception that the entire space 
surrounding any magnet is thus filled with “ Lines of Magnetic 
Force,” the filings on the plate merely serving to render the state 
of space adjacent to the magnet visible to the eye. In the C. G. S. 
system of units, a magnetic pole is defined as a magnet of such 



















316 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


strength as to repel an equal and similar magnet with a force' of one 
dyne, when the two poles are placed one centimeter apart. Coulomb 
expressed the law of magnetic action by the equation — 



(146) 




in which F is the mutual attraction or repulsion, m and m the 
strengths of the two poles, and d the distance between them. This 
expression is equivalent to asserting that the force between the poles 
varies as the product of the pole strengths, divided by the square of 
the distance separating them. If both poles have the same sign, the 
product is positive ; and, as repulsion exists, it is termed a positive 
quantity. Conversely, a negative sign would be applied to the force 
of attraction between two opposite poles. The strength or intensity 
of any magnetic field, at any point, is estimated by the effect which 
the field produces upon a unit positive magnetic pole placed at the 
point in question. Imagine a unit magnetic pole placed at any point 
in a magnetic field, and so disassociated from all matter as to be 
perfectly free to move. The direction in the field in which this 
hypothetical pole would then travel is termed the “ Positive direc¬ 
tion ” of the lines of force ; and the effort which the unit pole would 
exert in its motion is the measure of the magnetic strength, and is 
usually expressed by H. H varies from point to point in all mag¬ 
netic fields, though in large dynamos the field is so strong that H is 
sensibly uniform through the space under consideration, both in 
direction and magnitude. If, in every square centimeter of a field, 
the unit pole be acted upon with a force of one dyne, there is said to 
be “one line of Magnetic Force per centimeter,” and the field is said 
to have “one unit of Intensity.” When the intensity is H, there are 
H lines of force to each square centimeter ; thus the intensity of the 
magnetic field is conceived of as proportional to the number of lines 
of magnetic force passing through each square centimeter of surface 
perpendicular to the direction of the lines of force. 

386. Suppose a sphere to be described about a unit magnetic 
pole, having a radius of 1 cm. The surface of this sphere contains 
4 t r sq. cm. As, by definition, the unit pole emits one line of force 
through each square centimeter, 4 -n- lines of force will emanate from 
a unit pole ; and from a pole with the strength there will be 4 tt m 



CONDUCTORS FOR ALTERNATING CURRENTS. 


317 


lines of force. In air the number of lines is the same as the number 
of lines of magnetizing force, and for many other substances this 
proposition holds true. 

387. Some elements possess the property of greatly augmenting 
the number of lines, which are then termed “ Lines of Induction.” 
This is notably the case with iron. The sum of all lines per square 
centimeter, normal to the direction of the lines, is termed “The Total 
Induction, ’ and is denoted by B. In a non-magnetic medium B — H\ 
but in one that is magnetic, B > //, and the ratio of BjH is called 
the permeability, and is symbolized by /a. 

388. Faraday showed that every circuit carrying a current 
excites a magnetic field surrounding the conductor, in which the lines 
are closed circles inclosing the conductor. The sum of all the lines of 
force passing through the area inclosed by any electrical circuit is 
termed “The Total Induction of the Circuit,” and, when the circuit 
is placed away from magnetic media, is directly proportional to the 
current. 

According to the C. G. S. system, a unit current is one which, 
flowing in a circuit of 1 cm. radius, acts on a unit magnetic pole 
placed at the center of the circuit with a force of one dyne per square 
centimeter of length of the circuit. The ampere is one-tenth of the 
C. G. S. unit. If F be the number of lines threading a circuit, and 
/ be the current, then F varies as /, or F = LI , in which L is 
termed the coefficient of inductance, and may be defined as the ratio 
of the total inductance to the current producing it. Thus, in a cir¬ 
cuit of 2 cm. radius, carrying two units of current, there will be 
25.12 lines of force linked with the circuit; for, by definition, each 
unit length of the conductor acts on a unit pole at the center with 
one unit or one line of force per unit of current. As the conductor 
is 4 cm. in diameter, the length of the circuit will be 12.56 cm. ; and 
as there are two units of current flowing, there will be a total of 
25.12 lines of force linked in the circuit. 

In this case F = 25.12 ; I = 2 ; and hence, L will equal or 
12.56. Thus, if the geometrical dimensions of the circuit be known, 
the current flowing, and the permeability of the surrounding medium, 
it is possible to calculate the coefficient L. For ordinary cases, L 
is constant, and will be so considered. If the current is a variable 
one, changing from time to time, the relation of the current and 


318 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


the induction during any small interval of time is given by the 

equatlon - IL = N±. 

dt dt 


389 . Electro-Motive Force due to Varying Field. — Faraday 
proved that, when a conductor is so moved in a magnetic field as to 
cut the lines of force, the conductor becomes the seat of an electro¬ 
motive force directly proportional to the rate at which the lines are 
cut, and acting at right angles to the direction in which the con¬ 
ductor moves, so as to oppose, or obstruct, the motion of the con¬ 
ductor. From this, it is evident that to move a closed conductor 
in any magnetic field requires the expenditure of energy. Faraday 
further showed that, if the circuit be maintained stationary, and the 
magnetic field varied so as to increase or diminish the number of 
lines of induction, a similar result is obtained. Thus, at any instant, 
e — — dF / dt. In this equation, e symbols the electro-motive force 
developed at any instant, while the negative sign indicates that the 
direction of this electro-motive force is such as to oppose a change in 
the number of lines of induction that thread the circuit. A C. G. S. 
unit of E. M. F. is developed when there is a change in induction 
of one line per second ; and as this quantity is too small for conven¬ 
ient use, the volt is 10 8 times the C. G. S. unit. 

390 . Equation of Energy. — In Chapter VII. it has been demon¬ 
strated by Ohm’s law that, for circuits acted on by constant E. M. F.s, 
the current is 



in which E is the electro-motive force of the generator, E the resist¬ 
ance of the circuit, and e any opposing E. M. F.s. When a variable 
current exists in a circuit, the preceding paragraphs show that there 
is always an E. M. E. set up, due to the inductance of the circuit, 
that opposes the E. M. F. of the generator, having a value numeri¬ 
cally equal to — 


e 


dF 
dt ’ 


( 147 ) 


but, 


dF = Ldi . 
dt dt ’ 



hence, 


(148) 






CONDUCTORS FOR ALTERNATING CURRENTS. 


319 


The total energy supplied in a time T to a circuit is EIT watts. 
By Joule’s law, it is shown that I 2 RT watts are transformed into 
heat and dissipated by radiation. Throughout an infinitesimal of 
time, any E. M. F and any current may be considered constant. 
Also, by the principle of conservation of energy, the total energy ex¬ 
pended in a circuit in any time must be equal to the total energy 
delivered to it. The energy equation is, therefore, for the time cit — 


dividing by idt , 


eidt = Ri ~dt + Li — dt ; 

dt ’ 


e = Ri + L-. 

dt 



(150) 


In this equation, e is any instantaneous value of the E. M. F im¬ 
pressed by the generator on the circuit; Ri is the E. M. F. expended 

di 

in overcoming the ohmic resistance of the conductor ; Z, — is the 

E. M. F required to balance the counter E. M. F. set up in the 
circuit by the change initiated in the magnetic field by a constantly 
varying current. 

391. Expenditure of Energy. — As the current variations are a 
consequence of the varying impressed E. M. E, the counter E. M. E. 
of inductance is directly connected with, and is a function of, the 
impressed E. M. E. As the current varies from zero to a maximum 
/, the energy expended in heat during any complete current cycle 
is \ RI 2 , while that expended in the magnetic field is — 




Lidi = 1 LI' 2 . 


(151) 


B 




As that portion of the energy represented by i LI 2 is intimately 
connected with the nature of the vari¬ 
ations of the impressed E. M. F, it is 
now necessary to closely study their 
phenomena. 

Let the diagram, Fig. 206, repre¬ 
sent a uniform magnetic field, in 
which the lines of force are indi¬ 
cated by straight lines extending 
between the poles N and S. Suppose A to be the cross-section 
of a closed conductor revolving uniformly in the direction of the 
dotted circle. * The rate at which the conductor will cut the force 



Fig. 206. Diagram of the Motion of a 
Conductor in a Magnetic Field. 






























820 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


lines is seen by inspection to vary as the sine of the angle of ro¬ 
tation, being a maximum when the conductor is moving across the 
diameter NS, and a minimum when it is at right angles to this line. 
As the E. M. F. initiated is, at any instant, numerically equal to the 
rate of cutting, the E. M. E is a sine function of the angle of rota¬ 
tion, passing, in every revolution, through two zero points at B and 
C, and then through a positive and negative maximum at the inter¬ 
sections of the diameter NS. As the rotation is uniform, the 
E. M. F. is a sine function of the time of rotation. In practice, the 
curves of alternating electro-motive forces are found to closely 
approach the preceding proposition ; and even when the departure 
from a simple sine curve is considerable, by Fourier’s theorem, it 
may be demonstrated that any E. M. F. curve may be expressed as 



the sum of a series of terms, each of which is a simple sine function 
of the time of rotation. Consider now the curve of a sine function. 

392 . Harmonic Motion. — In the diagram of “ Harmonic Mo¬ 
tion,” Fig. 207, suppose the line AB to be pivoted at the point A, 
and to revolve about, in the plane of the paper, this point as a center. 
The end of the line B will trace the circumference FCDE. Assum¬ 
ing F as the starting-point, the projection of AB at any time, on the 
diameter CE, is AB sin BAF. When B is at F, the projection is 
zero. When B is at C, AB coincides with AC, the projection being 
a maximum equal to the radius of the circle. If the diagram be 
viewed edgewise, by placing the eye in the plane of the paper some¬ 
where in the prolongation of AF, the point B will appear to travel 
uniformly backward and forward along the line EC from E to C. 
Such motion is termed “ Harmonic.” The radius of the circle is the 
amplitude, designated by a , while the time T required to make a 















CONDUCTORS FOR ALTERNATING CURRENTS. 


321 


complete revolution is termed “The Period.’’ Positive rotation is 
reckoned as counter-clockwise, in the direction of the arrow. The 
crank of a steam-engine, when viewed from a point in the line pro¬ 
longing the piston-rod, or the motion of the bob of a clock pendulum, 
when seen from the point of suspension, are familiar examples of 
harmonic motion. If AB describes any angle <f> in a time / seconds, 
the angular velocity denoted by w is — 


— , or <b — co/, 

/ 

where to is the angle described in a unit of time ; also, as the entire 
circumference is described in the time T, — 

2 tt , , 2 tt/ 

w = —, and </> = —-. 


The number of revolutions in one second is 1 / T, and is designated 
as the “ Periodicity, or Frequency,” usually denoted by n. The angu¬ 
lar velocity may be expressed in terms of the frequency; that is to 
say, co = 2 7rand <j> = 2 tt nt. Reckoning time from F, when the 
projection of AB on AC is zero, and denoting the projection on AC 

^ y* y — a sin (f) = a sin co/. 


and y is a sine, or harmonic function of the time. If the time inter¬ 
val be reckoned from some other point, say P, then there is an angle 0 
between this point and the point of zero projection F. This angle is 
termed “The Angle of Epoch,” and the angle <f> + 0 is called the 

phase. In this case- . , , , 

^ y = a sin (<£ + 0) ; 

or, y = a sin (co/ -f 6). (152) 

393. When 0 is positive, measured from F in the direction of the 
arrow, it is often called the “Angle of Advance.” When it is nega¬ 
tive, measured clockwise from F to some point P", it is termed 
“The Angle of Lag.” It is readily seen that when the angle of phase is 
zero, AB coincides with AF, and the projection on y is zero.' When 
the phase is 90°, and AB falls along AC, the projection is a positive 
maximum, and y = + a. At 180 ° y is again zero, and All coincides 
with AD, and lastly at 270°, y = — a , a negative maximum AB 
coinciding with AE. With every revolution this cycle is repeated. 
Conceive now that while AB is revolving about A, the paper be 
moved steadily and uniformly in a direction contrary to the arrow 
mark, while A remains stationary. The point A will trace a line 












322 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


' GH, while the point B will trace a sinuous line KRMSO. As the 
motion of the paper is uniform, the distances along GH will repre¬ 
sent intervals of time, while the vertical distances between GH and 
the points of the curve will represent successive projections of AB 
on AC. In the diagram, the various elements of the curve are repre¬ 
sented, as follows : — 

Generating point B. 

Circle of revolution FCDE. 

Axis of time GH or axis of x. 

Amplitude a = AB = AF = KL = LR. 

Angle of advance 0 = PAF = Angle of epoch. 

Angle of lag — 0 = FAP". 

Angle described in time / = <f> — PAB. 

Angle of phase 6 + <f> — FAB. 

Time of epoch K/'. 

Time of phase i 4- K p' = Kb'. 

394. The point B in the diagram may represent the cross-section 
of any one of the armature conductors of the common dynamo, and 
so the path described by this and all other armature conductors will 
coincide with that in which B moves. As the E.M.F. initiated in 
each conductor is proportional to the rate at which the lines of the 
magnetic field are cut, and as this rate varies according to the sine 
of the angle of rotation, the sine curve KRMS is representative of 
the periodic variations of the E.M.F. set up in the conductor. As 
the E.M.F. is constantly varying, the current will be correspondingly 
periodic, and the locus of its curve will be a line similar to the curve 
KRMS. 

395. Average Values. — If, in the equation — 

y — a sin («/ + 0), 

E or / be substituted for a , y becomes the value of the E.M.F. or 
current at any given instant. 

e = E sin («/ -f- 0) ; (153) 

i = /sin (o ot 4- 6). (154) 

In practical work the average values of these quantities are much 
more in demand than the above instantaneous values. As a sine 
curve is a succession of similar and equal positive and negative 
cycles, the average ordinate for any period, or succession of periods, 









CONDUCTORS FOR ALTERNATING CURRENTS. 


323 


is algebraically zero; but as the latter half of each period is the same 
as the first with its sign reversed, the average ordinate for any half 
period will be the arithmetical mean ordinate. During a half period, 
indicated by T / 2, a certain quantity Q of electricity will flow through 
the circuit, and the alternating current may be compared to a steady 
current which would deliver the same quantity of electricity through¬ 
out the same circuit, in the same time. If 3 is this current- then — 


5 = ^ 1 = C 2 idt ; 

L JO 


but, 

i 

whence 


and 

3 = 


IT 


IT 


2 I 

7r 


(155) 


(156) 


•Thus it appears that a continuous current necessary to deliver in the 
same time the same amount of electricity as an alternating one, will 
have .6369 of the value of the maximum ordinate of the alternating 
current. 

396. Alternating currents may also be compared to continuous 
currents by noting the relative thermal or chemical effects produced. 

‘ Any current, whether alternating or continuous, in traversing a con¬ 
ductor evolves heat at a rate which is measured by 3 2 RT. The 
readings of a Cardew voltmeter are obtained by noting the heating 
effect produced in a long, even, high resistance wire. As the ther¬ 
mal effect is proportional to the square of the current, and as the 
current is proportional to the voltage, it is evident that the instru¬ 
ment really measures the mean square of all the instantaneous 
current values that occur while the measurement is being made ; and 
if the relation of the mean square to the maximum value be known, 
the readings of the voltmeter will furnish the necessary data to 
calculate the E.M.F. curve. By Joule’s law, the heat evolved is 
% 2 RT ; hence, during half a period, — 


¥R I = f 7 i 2 Rdt ; 

2 Jo 


(157) 


replacing i by its value from equation (154), 


3 2 R — = R I' 1 f ? sin 2 (cot + 0) dt . 
2 Jo 


3 = 


I 

V2 


= .707 /. 


(158) 





324 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Thus it appears that the arithmetical mean electro-motive force or 
current is less than that indicated by the Cardevv voltmeter, or other 
similar instrument; for, from equation (156), the arithmetical mean 
is .6369 ; and from the preceding equation (158), the square root of 
the mean squares is .707, and the difference, .071, is about ten per 
cent. Having the voltmeter readings, the maximum electro-motive 
force may be obtained by multiplying the voltmeter value by 1.415. 

397. The Solution of the Energy Equation. 


A. CIRCUITS CONTAINING RESISTANCE AND INDUCTANCE. 


Having thus considered the elementary properties of the curve 
of harmonic motion, the way is prepared for a general solution of the 
equation representing the balance of energy in an alternating current 
circuit. Referring to Fig. 207, assume t to be reckoned from F, and 
E = AB, then, e = E sin c ot ; also, as has been proved, — 


e = Ri + L 


di 
dt ’ 


hence, 

transposing, and dividing by Z, 


di 


Ri 4- L — = E sin cot: 
dt 


(159) 


di . R . E . 

-- i = — sin cot. 

dt L L 


(160) 


This is a linear differential equation of the first order, of which the 
general type is, — ^ 


dx 


The solution 1 of such an equation is, 


—fpdx 
- d 


y = e 


[j'Qd Pd ‘</ x + C], 


Substituting the values of the coefficients derived from equation 
(159), and performing the integration indicated in the exponents 

of ~ * r 

T 


yr —to I* B _ia 

i — — e l I e l sin cot dt -f- Ce l . 


L 


Integrating by the rules for exponential functions, 2 and reducing to 
simplest form, — 

E ( r m\ -Rt 

‘ = V ** + z V sin f ~ tan_1 T ) + a ~ L - 


1 See Carr's Synopsis of Pure Mathematics , p. 472, art. 3110. 

2 Carr, Synopsis of Pure Mathematics , p. 325, art. 1998. 






CONDUCTORS FOR ALTERNATING CURRENTS. 


325 


It can be shown 1 that the constant of integration which contains the 
exponential term applies to the circuit only for a minute period of 
time immediately succeeding the first application of the E.M.F. 
This term may therefore be disregarded in a consideration of the 
constant regime of an alternating current circuit ; the equation there¬ 
fore reduces to — 


i 


E 


VZ 2 -f ZW 


sin 


w/ — tan 1 



(161) 


398- This equation indicates, — 

First. An harmonic impressed E.M.F. in a circuit containing 
resistance and inductance produces a current that is a sine function 
of the periodic time. 

Second. The current lags behind the E.M.F. by an angle of 
which the tangent is Zco / R. 


Third. When sin — tan~ 1 
maximum value, and — 

/ = 


L 


0) 


R 

£ 


VZ-f E-m- 


= 1, the current attains the 


(162) 


The quantity Lw is called “Reactance,” and the quantity V R 2 -f Z 2 to 2 , 
the apparent resistance of the circuit, is denominated “ Impedance,” 
often symbolized by J, and will be more fully treated under the sec¬ 
tions on “Graphical Methods.” If this quantity be substituted for R 
in Ohm’s formula when applied to alternating circuits, his equation 
will hold true. 

Fourth. If L = 0, the equation reduces to i — F sin cot / R 
which accords directly with Ohm’s law. Impedance, as deduced 
from this expression, causes the current to lag behind the impressed 
E.M.F. , and reduces its successive values. 

E 

Fifth. If R = 0, i = t— sin («/ — 90°), indicating that when the 
J L o) 

resistance is so small as to be negligible, the current cannot exceed 
E / Z&), and then lags 90° behind the impressed E.M.F. 

Sixth. If either R or L become indefinitely large, the current 
reduces to zero. 


1 Fleming, Alternate Current Transformer, p. 102. 









326 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Sec. b .— The Effect of Mutual Inductance. 

399. If a circuit A is placed in such a manner as to be in close 
proximity to a second circuit B, that carries an alternating current, 
the varying magnetic field initiated by the B circuit will react on 
the A circuit and set up therein an E.M.F. If it be imagined that 
two circuits are so close together as to occupy the same space, it is 
evident the total induction of the B circuit will pass through the A 
circuit, and the E.M.F. set up in the A circuit will be equal to the 
inductance of the circuit, and may be represented by L B . If the 
conditions be reversed, and the current be assumed in the A circuit, 
its inductance will act in a similar manner on the B circuit, with an 
effect to be measured by Z 4 . Now, if current flows in both cir¬ 
cuits, each will react upon the other, proportionally to the current in 
each. In this hypothesis, the two circuits are assumed to be so 
close together that all the lines of force generated by each will be 
linked with the other, and the coefficient M of the mutual inductance 
may be defined as “ The total induction, linked with both the cir¬ 
cuits, divided by the sum of the currents in both circuits.” If, as 
in the previous supposition, two circuits are supposed to coincide in 
space, it is evident that — 

M < or = L a , 

M < or = L b ; 

therefore, J/ 2 < or = Z J Z jS . 

and the maximum possible value of M is the square root of the pro¬ 
duct of the inductances. 

B. THE GENERAL EQUATION OF ENERGY FOR MUTUALLY INDUCTIVE CIRCUITS. 

400. For a simple circuit having resistance and inductance in 
series, the energy equation has two terms, Ri 2 denoting the portion 

. di 

transformed into heat, and Li — measuring the amount expended in 

the magnetic field. When there are two or more circuits in close 
proximity, a portion of the magnetic field created by each will be 
employed in inducing an E.M.F. in the other circuits, and may be 
measured by the product of the coefficient of mutual inductance and 
the current. Consider the case of two circuits A and B with im¬ 
pressed E.M.F.s E a and E B , with resistances R A R B , inductances 


CONDUCTORS FOR ALTERNATING CURRENTS. 


327 


L a L b , currents I A I Bf and a mutual inductance M, then for circuit 
A the energy equation is — 

E A dt = R a Ifdt + L a ] A dI A + MI A dI B ; (163) 

and for B, 

E B dt = R b Ifdt + L B I B dI B + M I B dI A ; (164) 

adding, 

(E a + E b ) dt = (R A If + R b I*) dt + L A I A dI A + L B / B dI B + M(I A dI B 
+ C B dI A ). (165) 

The first term on the right-hand side of equation (165) is the heat¬ 
ing effect, the second and third are the energies expended in induc¬ 
tance, while the fourth is that due to mutual reaction ; but the second, 
third, and fourth terms form the exact differential of — 

T / 2 7 jrs 

+ M I A A, 

+J £ 

and the equation for the circuits reduces to — 

E a + E b = \ {L a / a + L b I b ) + MI a I b + R a I a + R b I b \ (166) 

An extension of the same process may be used when there are 
more than two circuits. Usually alternating circuits can be so 
designed and erected as to reduce mutually inductive effects to so 
small values that they may be neglected. Exceptions occur in the 
construction of dynamo machinery. Rarely more than two circuits 
are involved, and usually only one of the two is subjected to an 
impressed E.M.F. In such cases the presence of iron renders the 
introduction of the permeability factor /x essential. This subject 
will be further expanded in the sections on Graphical Methods. 

401. Coefficients of Inductance. — Conformably with the C. G. S. 
system, inductances are lengths, and theoretically can be com¬ 
puted from the geometrical relations of the circuit. As the process 
of calculation is sometimes tedious, the most useful values are here 
appended. Several units have been in vogue for inductance. Eng¬ 
lish and Continental electricians have been in favor of adopting the 
term “ secohm ” or “ quad,” being the equivalent of 1,000,000,000 cm. 
of length or an earth quadrant. In this country the term “ Henry ” is 
authorized for the same value. In many respects, inductances be¬ 
have like resistances, absorbing from the circuit a certain amount of 
energy. Unlike resistance, this energy is not transformed into heat ; 
but in some, at present unknown, manner, is stored in the mag- 




328 THE ELECTRICAL TRANSMISSION OF ENERGY. 

netic field, and when the circuit is interrupted, appears in the form 
of the well-known extra current. In the following values, the cir¬ 
cuits are assumed to be of non-magnetic material, and to be immersed 
in a non-magnetic medium, in which the permeability /x = 1 ; when 
the composition of the circuit, or when the circuits, are adjacent to 
materials in which the permeability differs from the above values, 
the necessary permeability factor must be introduced in all of the 
formulae. In the expressions, C. G. S. units are employed, 1 (length), 
d (distance), r (radius), all in centimeters ; and the values obtained for 
the coefficients are likewise in the same unit. To reduce these values 
to “henrys,” the value of L should be divided by 1,000,000,000. 
The currents also are in C. G. S. units, and must be changed where 
amperes are used, by multiplying by the proper value. Mutual 
inductance is symbolized by M } and self inductance by L. 

First . Inductance of a circuit of two long parallel copper wires 
of radius r, and interaxial distance d per unit of length 

L = lL 5 + 21og,^V 

When the length of the circuit is /, or half the length of the con¬ 
ductor measured around the loop, the total inductance is — 

L = 2 /(.5 + 2 log, -)• 

Second. Coil of a single layer; / = length of coil, n = number of 
turns, r = radius of coil. 

L = 4 t r W 
/ 

Third. Coil of several layers ; / = length of coil, R = radius of 

outer layer, r = radius of inner layer, n = number of turns. 

4 7T 2 // 4 

L = W7T- (* ~ r) (^ 3 ~ **)• 

Fourth. Coil in the form of a ring; A = radius of the ring, 
a = radius of the coil, n = number of turns. 

L = 2 7 T/i 2 (A — V A* — a 2 ). 

Fifth. If a second coil be formed on the first, having m turns of 
wire, the mutual inductance is — 


M = 2 7 Trim (.A — f A 2 — a 2 ). 






CONDUCTORS FOR ALTERNATING CURRENTS. 


329 


Sixth. Two wires wound parallel to each other, having a length 
/, and radii r and r\ and having a distance between centers of b. 

L — 2 l ^.5 -f- log, —— f ^ . 

Seventh. Mutual inductance of two concentric coils ; / = length, 
the outer one having m turns, the inner one and a radius of r. 

m= UCNil. 

I 

Eighth. Two circles each of a radius r, parallel to each other, and 
separated by a distance d , have a mutual inductance of — 


M 


7 rr 


i , 3 d* , 

1+ 16^ + ' ' ' 


i 8 r . 

log*-4 7rr 

d 


d 2 

2 + N-.+ ■ ■ • 


1G 





402. Case 3 : Effect of Capacity. — If any very carefully insu¬ 
lated conductor be connected to any source of electrical energy, a 
uniform distribution of potential rapidly takes place, all parts of the 
conductor presently arriving at that of the source of supply. Exper¬ 
iment and theory indicate that the change in the potential of the 
different parts of the conductor, necessary to accomplish the condi¬ 
tion of potential equality with the source, is accompanied by the 
transfer of a certain quantity of electricity. If the potential of the 
source is greater than that of the conductor, the transfer is from the 
source to the conductor, while if the converse be true, the electrical 
movement is in the inverse direction. The amount of electricity 
which, under these circumstances, can be received by a body meas¬ 
ures its “Capacity.” In the C. G. S. system the capacity of a body 
is measured by the quantity of electricity that is absorbed during an 
increase of potential of one C. G. S. unit, between the body receiving 
the charge and that of its surroundings. The unit of capacity is the 
Farad, and is that amount of capacity which, when charged with one 
coulomb of electricity, will exhibit a difference of potential of one 
volt. So large a capacity as a farad exists only in imagination ; for 
the capacity of the earth is only about .0007 farad, and that of the 
sun .076 farad. Practically, the Microfarad, or the one-millionth of 
a farad, is usually employed. 

The capacity of any conductor depends upon its size and shape ; 
and upon the size, shape, proximity, and state of insulation of neigh¬ 
boring bodies ; and the nature of the dielectric that separates them. 











330 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Also, as electricity behaves as if it possessed elasticity, capacity is 
not a constant quantity, but depends upon the potential acting in the 
circuit. By increasing the surface of the conductor, and decreasing 
the distance separating it from neighboring conductors, capacity is 
augmented. Arrangements of conductors to attain the greatest pos¬ 
sible capacity are called “ Condensers," of which the common Leyden 
Jar, or a collection of metal plates separated by thin sheets of dielec¬ 
tric, are familiar examples. The capacity of a condenser may be 
determined from the formula 1 — 

c = -A—, 

4 tu i 

in which 5 is the area of the plates, d the distance between them, 
C being the capacity in electrostatic units. 

403. Suppose a simple circuit containing a condenser in series 
with resistance. During the first few infinitesimals of time succeed¬ 
ing the establishment of difference of potential at any part of the 
circuit, electricity flows into the line and is absorbed by the con- 
denser. During the time of charge, the difference of potential at the 
terminals of the condenser gradually rises until it equals that of the 
generator, and then the flow of current stops. A parallel example 
could be drawn by imagining a steam-boiler to be connected by a 
long pipe to a tank, or reservoir. On opening the valve the steam 
will flow into the tank until the pressure in the tank equals that of 
the boiler, when the flow will cease. Also, the higher the boiler 
pressure, the greater the quantity of steam that will be forced into 
the tank. When the pressure is equalized no further flow takes 
place, excepting a slight transfer necessary to compensate for con¬ 
densation or leakage. As no electric circuit is perfectly insulated, 
the parallel is still closer, as after the condenser is charged there 
still remains a slight flow to compensate for poor insulation and 
dielectric leakage. 

404. Now, consider the case of an alternating current circuit, 
under an harmonic E.M.F, that with every cycle constantly varies 
between a plus and minus maximum. Throughout one part of the 
cycle the current is gaining strength from the minus maximum to 
the plus maximum, and the difference of potential at the terminals of 
the condenser is thereby being constantly increased. Throughout the 


1 See Barker’s Physics, p. 560. 



CONDUCTORS FOR ALTERNATING CURRENTS. 


331 


other half, as the impressed E.M.F. is decreasing, the condenser is 
discharging itself into the circuit, and returning some of the energy 
previously absorbed. If, in the steam-boiler example, the pressure 
in the boiler be imagined to undergo a periodic variation, there would 
be backward and forward flow between the boiler and the tank, and 
the tank and boiler, in each cycle.. 

Throughout every period of any alternating circuit, a certain 
quantity of electricity is set in motion by the impressed E.M.F. 
Manifestly, if a condenser of sufficient size to absorb, under the poten¬ 
tial of the impressed E.M.F, this quantity of electricity, the presence 
of such a condenser in the circuit will not effect the apparent quan¬ 
tity of the current. By definition, capacity is a function of the acting 
E.Ad.F, or in other words, the potential at the terminals of the con¬ 
denser is proportional to the charge it contains. Hence, the poten¬ 
tial at the condenser terminals in any such circuit is an harmonic 
sine function of the period of the circuit; and the condenser acts, to 
introduce into the circuit an additional E.M.F ., of which the account 
must be taken in a consideration of current and potential distribution. 

405. The Solution of the Energy Equation for Circuit with 
Capacity. 


C. CIRCUITS CONTAINING RESISTANCE AND CAPACITY. 


As the capacity of a condenser is the amount of electricity in 
one conductor, when there is a unit difference of potential between 
the pair of conductors forming the combination, the charge q at any 
other potential E will be— 

r q — CE, (167) 


C being the capacity of the condenser. The energy W expended 
in charging a condenser can be shown 1 to be W =\q 2 ‘ / C\ differ¬ 
entiating, — dW = qdq 

C 


( 168 ) 


The total energy delivered to a circuit in a time dt is eidt. When 
there exist resistance and capacity but no inductance, this quantity 
must be spent in heat and in charging the capacity. The heat 
expenditure is measured by Ri 2 dt. That stored in the condenser is 


plainly 7 ^ dt ; hence, the energy equation is — 


Cdt 


eidt = Ri-dt + qdq - dt. 

Cdt 


( 169 ) 


I Barker’s Physics, p. 566. 





332 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


With a current i flowing for a time dt, a quantity of electricity 
idt will pass into the condenser, hence — 

idt = dq, or q — Jidt ; (. TO) 


therefore, 

dividing by idt , — 


eidt = Ri 2 dt A - idt 

C 


J 1 idt ; 


Ri -f- — ^idt, 


(171) 


an equation resembling that applying to circuits containing resistance 
and inductance. Differentiating to get rid of the sign of integration, 
and transposing, — 


di 1 de , i 
dt ~ ~R~dt + RC 


= 0 . 


Remembering that e = E sin o>t, and employing a similar method 
of solution to that indicated on p. 324, and neglecting the constant 
of integration, — 

W 2+ c 


sin o)t + tan 


—i 


RC 


O) 


(172) 


W 


406. This equation indicates — 

First. That an harmonic impressed E.M.F. in a circuit contain¬ 
ing resistance and capacity gives rise to a current that is an har¬ 
monic sine function of the periodic time. 

Second. The current is in advance of the E.M.F. by an angle of 
which the tangent is 1 / RCgj. 

Third. When sin (wt + tan -1 1 j RCE) becomes unity, the cur¬ 
rent attains its maximum value, and — 



(173) 


The quantity s/R' 1 -f- 1 / C 2 m 2 is the apparent resistance of the cir¬ 
cuit, termed “ Impedance,” often symbolized by _/, and will be more 
fully treated in the sections on “Graphical Methods.” If this quan¬ 
tity be substituted for R in Ohm’s formula, the equation will hold 
true when applied to alternating currents. 1 / Cm is the “ Reactance 
of the Circuit.” 

Fourth. When C diminishes to 0, i becomes 0. Such a condi¬ 
tion obtains when the size of the conductor is indefinitely decreased, 
or the thickness of the dielectric indefinitely increased. 












CONDUCTORS FOR ALTERNATING CURRENTS. 


338 


Fifth. If R = 0, the equation reduces to 


i 


E 

1 / Cm 


sin (a )/ -f- 90 °) = CmE sin («/ -f- 90 °), 


( 174 ) 


showing a current 90 ° in advance of the impressed E.M.F., with a 
maximum value numerically equal to CmE. If the resistance of the 
circuit be so small as to be negligible, the above condition is attained 
when the condenser is short-circuited. 

Sixth. If R increases to infinity, i reduces to 0, but if C in- 

1 


creases, tan 


—1 


CRm 


decreases, and at C = 00 the formula becomes 


i — E / R sin Mt, thus reducing to Ohm’s equation, with the current 
in phase with the impressed E.M.F. Such a condition occurs when 
the thickness of the dielectric is reduced to zero, and the condenser 
plates touch each other. The interpretation of this result is found 
in the statement that under such circumstances no charge, no 
matter how large, can produce any difference of potential between 
the plates. Making the condenser infinitely large is equivalent to 
removing it from the circuit. Compare these deductions with those 
derived from equation (161). 

The symbol m has been employed as an abbreviation of 2? m ; but 
this quantity is the distance traveled by the generator point B (see 
Fig. 207) in one second of time, when the radius of the generating 
circle, or amplitude, is unity. When the amplitude has any other 
value, it must be introduced into the above expression. As both 
inductance and capacity are expressed in units of length, the expres¬ 
sions for the reactance Lm , or 2irnL f and 1 / Cm, or 1 / 2-n-nC, are dis¬ 
tances. If L and C be thought of as the radii of the generating 
circle, Lm and 1 / Cm are values of the speed at which the generating 
point is traveling. Mr. Kennedy has very aptly termed these values 
the “ Inductance Speed ” and the “ Reciprocal of the Capacity 
Speed.” 


D. THE ENERGY EQUATION FOR CIRCUITS CONTAINING RESISTANCE, 

INDUCTANCE, AND CAPACITY. 

407. In the energy equation for a circuit with resistance and 
inductance, — 

E 

1 =--sin 


V R 2 + ZW 


Mt — tan 1 iCL 
R 







334 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Suppose Lm to be equal to Em + L"w then — 


i — 


E 


- sin (&)/ — tan 


V R 2 + (Em 4- E'm) 2 

now, for E'm substitute — 1 / Cm, and — 

E 


_ x L'm -f- E'm 
R 


i — 


V +1 


sin 


o)/ —|— tan 


-i 


1 _ L'm 


CRm R 


408. This equation indicates — 

First. That both current and charge are simple harmonic func¬ 
tions, and may either lag behind the impressed E.M.F. or be in ad¬ 
vance of it, depending as to whether Em > or < 1 / Cm, the algebraic 
sum of these quantities determining the tangent of the angular rela¬ 
tion of the current and impressed E.M.F. 

Second. If Em = 1 / Cm, the two quantities neutralize each other, 
and the current is in phase with the E.M.F. ; the equation then 

reduces to — „ 

i = — sin &)/. 

R 


It is thus evident that a judicious relation of inductances and capaci¬ 
ties may be employed to adjust the angular relation of current and 
E.M.F. in any desired fashion. 

Third. When the sine becomes unity, the maximum value of the 
current is reached, as — 



409- The quantity — 

N+m 

is the “ Impedance of the Current,” and behaves like a resistance ; 
for when this quantity is substituted for R in Ohm’s formula, it 

applies perfectly to alternating circuits. The quantity Em — -yr~ is 

the “ Reactance,” to be more fully treated in the paragraphs on 
“ Graphical Methods.” 

Fourth. Either R, L, or C may vary from 0 to oo , and resulting 

* 

current determined by the principles already indicated as applying 
to the limits of these quantities. 



















CONDUCTORS FOR ALTERNAT/NG CURRENTS . 


335 


Fifth. In a circuit containing resistance, inductance, and capacity, 
the impressed E.M.F. is expended in balancing three quantities : the 
heat losses, measured by RF 2 ; the reactance due to inductance, esti¬ 
mated by LmI ; and that due to capacity, equal to 11 Cm. It is easy 
to see that // Cm can have such a value as to cause this component 
of the E.M.F. to exceed, numerically, the impressed E.M.F. 

410. Graphical Methods. — While the preceding paragraphs 
have given an outline of the algebraic treatment of alternating cur¬ 
rent circuits essential to an elementary conception of the subject, 
the same problems may be handled geometrically by graphical 
methods. In many cases, these methods are far simpler than ana¬ 
lytical solutions, and always present the advantage of appealing 
directly to the eye in such a manner as to insure immediate detec¬ 
tion of error. Electrographics has already received considerable 
attention from many eminent electricians, 1 to which the reader is 
referred for more detailed descriptions. As alternating current prob¬ 
lems are most conveniently handled by the use of vectorial algebra, 
it is advisable to define the elementary uses of vectors before pro¬ 
ceeding to the consideration of the problems. 

411. Vector Quantities. — When the symbols of ordinary alge¬ 
bra are assigned a definite meaning, they usually become scalar 
quantities, that is, quantities which simply have a numerical value, 
or are mere numbers. When dealing with geometrical magnitudes, 
it is not only necessary to consider the numerical value of various 
lines, but also to consider the direction of each line. A vector quan¬ 
tity, therefore, is one in which the direction of the quantity is con¬ 
sidered as well as its scalar magnitude. Direction is considered as 
positive when it is reckoned upwards, and negative when it is down¬ 
wards from a horizontal base line. Right-handed rotation is negative, 
and left-handed positive. Suppose AB, No. 1, Fig. 208, “Diagram 
of Operations on Vectors,” to be a straight line of two units in length, 
inclined at an angle of 35 ° to the base line AC. Let DL, No. 2, be 
any other straight line inclined at an angle of 75 ° to the same base 
and of four units in length. These lines are plain vectors, of which 
the scalar magnitudes are, respectively, two and four units. 

1 See Fleming’s Alternating Current Transformer; Blakesley’s Alternating Currents; 
Kapp’s Dynamos , Alternators , and Transformers; Gerard’s Lemons sur Z. Electricite , Rennelly 
Trans. A. I. E. E., April, 1893, and Electrical World , vol. 22, p. 300 ; vol. 23, p. 17; Rimming- 
ton, Electrical Review for 1893, p. 064 ; Emmett’s Alternating Current Wiring. 



336 


THE ELECTRICAL TRANSMISSION OF ENERGY 




Fig. 208. Diagram of Operations on Vectors. 











CONDUCTORS FOR ALTERNATING CURRENTS. 


337 


412. —The addition of vectors is accomplished by joining them 

end to end and then connecting their extremities ; the line connect¬ 
ing the extremities, being the vector sum of the two vectors to be 
added. I hus, to add AB and DE, draw A'B', as in No. 3, parallel 
and equal to AB, and from B' draw B'E' parallel and equal to DE 
and join A'E'. 1 hen A'E' in direction and magnitude is the sum of 

AB and DE. In this case AB plus DE equals 5.7, and is inclined 
to the base line at an angle of 62° 30'. 

413 . — Similarly, subtraction is performed. Thus, to perform 
the ope ration DE — AB, draw, as in No. 4, D'E' equal and parallel 
to DE. From E' lay off E'A' equal and parallel to AB. Join D'A'. 
1 hen D'A' measured positively is the desired result ; in this case 
D'A" =2.8, and is inclined to the base at 101° 30'. To perform 
the operation AB — DE, draw, as in No. 5, A'B' equal and parallel 
to AB. hrom B' draw B'E', negatively , equal and parallel to DE. 
Join A'E'. In this case A'E' has the same numerical value as in 
No. 4, but it is a negative quantity, and not a positive one, as in No. 
4. Also in No. 4 the angle of inclination is positive and 101° 30', 
while in No. 5 it is negative and is 78° 30'. 

414 . — Multiplication of vectors is performed by multiplying the 
scalar magnitudes and taking the sum of their angular directions. 
Thus, the product of AB and DE is the plain vector EG, No. (3, 
equal to 2x4 = 8 units in length, and inclined 35 -f- 75 = 110° to 
the base line. 

415. — Conversely, division is performed by dividing the scalar 
magnitudes, and taking the difference of the angles. Thus, in No. 
7, DE / AB = 4/2 = 2, inclined at an angle of 75° — 35° = 40° to 
the base line. Also, in No. 8, AB / DE = 2 / 4 = .5, inclined at an 
angle of 35° — 75° = —40°. 


416. — The reciprocal of the vector is a plain vector having a scalar 
magnitude equal to the reciprocal of the scalar of the original vector, 
but inclined to the base line at the same angle as the original vector. 

417. —The solution of the following problems will now be given : 

1. Composition and resolution of electro-motive forces. 

2. Electrical properties of simple circuits with one resistance 
and one inductance in series. 

a. The resistance variable. 

b. The inductance variable. 





















338 


TIIE ELECTRICAL TRANSMISSION OE ENERGY. 


3. Electrical properties of simple circuits with several resist¬ 
ances and inductances in series. 

4. Electrical properties of simple circuits with one resistance 
and one capacity in series. 

a. Resistance variable. 

b. Capacity variable. 

5. Electrical properties of simple circuits with several resist¬ 
ances and capacities in series. 

6. Electrical properties of simple circuits with resistance, in¬ 
ductance, and capacity in series. 

7. Electrical properties of simple circuits with several resist¬ 
ances, inductances, and capacities in series. 

8. Electrical properties of circuits with resistance, inductance, 
and capacity in multiple arc. 

9. Electrical properties of mutual inductive circuits. 

418. 1. Composition and Resolution of Electro-Motive Forces. 
— For continuous current circuits it has been shown that the effect¬ 
ive E.M.F. was equal to the algebraic sum of all the E.M.F.s acting 
on the circuit. For alternating currents it must now be proved that 
a similar proposition holds true, provided the vector, or geometrical 
sum, is taken. 

In “Diagram of Composition of E.M.F.s ,” Fig. 209 , suppose the 
line AB represents one E.M.F. acting on a circuit, and AB' repre¬ 
sents another, the two E.M.F.s to have the same period, and sepa¬ 
rated by angle BAB’. Draw BB" and B'B" respectively equal and 
parallel to AB' and AB, forming the parallelogram AB'B"B. 
Draw the diagonal AB." Since BB" is equal and parallel to AB', 
the projection of BB" on AC is equal to the projection of AB' ; that 
is, y y" = Ay. The projection of AB_ is Ay, hence the sum of 
the projections of AB and AB' is Ay" , and, from the geometry of 
the figure, this is equal to the projection of AB", or the projection 
of the diagonal of the parallelogram. Suppose the parallelogram 
AB'B"B revolves about A as a center, all of the lines retaining- the 
same angular relation. The sum of the projections of AB and AB' 
will, in every position, be the projection of AB" ; and as these lines 
revolve harmonically, they will trace three sine curves, indicated by 
the heavy line, the light line, and the dotted line, numbered I, II, 
III. As BB" is equal and parallel to AB', it will be at once per- 















CONDUCTORS TOR ALTERNATING CURRENTS. 


389 


ceived, by the previously outlined rules for vector quantities, that 
AB" is the vector sum of AB and AB' ; hence the sine curve III, 
is the vector sum of I and II, and at all points represents the result¬ 
ant of the harmonic E.M.F.s acting on the circuit. Should more 
than two E.M.F.s act on a circuit, the same train of reasoning may 
be extended by selecting any two E.M.F.s and combining them 
into a single, resultant curve. This resultant and any other E.M.F. 
may then be united into a third resultant, and the process repeated 
until the final curve is obtained. In a like manner it can be shown 
that any number of E.M.F.s of varying periods may give rise to a 
single resultant E.M.F, while the converse of this proposition is 
equally obvious; namely, that a single E.M.F. may be resolved into 
any two components. The similarity between this construction and 



that employed by the science of mechanics, in the parallelogram of 
forces, is obvious. If, therefore, in a complex circuit, the E.M.F.s 
in the various branches are given in magnitude and direction, the 
resultant E.M.F., or that which it is necessary to impress on the 
circuit, is readily deducible. Given the electrical properties of the 
various branches of a compound circuit and the several currents 
required, the impressed E.M.F. may be decomposed into com¬ 
ponents having magnitudes and directions suitable to produce the 
desired currents in each branch; or, finally, given the resultant 
E.M.F., and all but one of the components, the missing component 
may be found, and the electrical relation of the circuits adjusted to 
suit. In the solution for the Energy Equation, as applied to circuits 
containing resistance, inductance, and capacity, it was shown that 
the energy delivered to the circuit split into three parts, the RI 
component in phase with the current ; E»I, 90° behind the current, 






340 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


and // Cm 90° in advance. As these components may assume a 
great variety of values, and as in multiple arc circuits other phase 
relations may obtain, it is easy to see that the maximum values of 
the components may be greater, equal, or less (numerically), than 
that of the resultant. The geometrical construction will always, in 
a clear and simple manner, elucidate any case of this description. 

419. 2. Electrical Properties of Simple Circuits with One 
Resistance and One Inductance in Series. — Referring to Fig. 207, 


Fig. 210. Diagram of a Simple Circuit 
Containing Resistance and 
Inductance. 


Resistance R = 40 ohms 


“ Diagram of Harmonic Motion,” assume that the full line KRMSO 
represents the current curve due to an harmonically varying E.M.F. 
in a simple circuit having resistance and self-induction. The counter 
E.M.F, due to self-induction of the current, originates in the varying 

magnetic field set up by the 
changing current, and is di¬ 
rectly proportional to the 
rate of change of this field. 
The rate of variation of the 
current, at any time, is 
measured by a tangent to 
the curve at the point of 
time under consideration. 
A simple inspection of the 
curve indicates that the max¬ 
imum value of this tangent 
occurs at the points O and 7 r, while at 7 - j 2 and 3 7 r j 2 ; the tangent 
is horizontal, and its value 0 ; therefore the points K and M corre¬ 
spond to the maximum ordinates of the curve of E.M.F. due to induct¬ 
ance, indicating that this curve is similar to the current curve in 
period and shape, but lags behind it at an angle of 90°. Such a curve 
is represented by the dotted line cutting the axis of X 90° behind the 
current curve. It is, therefore, possible to represent geometrically 
the relations of an alternating current circuit containing resistance 
and inductance, by a right-angle triangle. In Fig. 210, “ Diagram of 
E.M.F. in a Simple Circuit Containing Resistance and Inductance,” 
draw a line horizontally from A to B in a positive direction. At A 
lay off AB to any convenient scale, equal numerically to R. At B 
draw BC perpendicularly and positively to AB, and lay off BC to 
the same scale of a value equal to Lm. Draw AC, then AC to the 






CONDUCTORS FOR ALTERNATING CURRENTS. 


841 


same scale represents the R 2 -f- Considering the equation 

I VR 2 + L 2 or = E, it is seen that the impressed E.M.F. may be 
divided into two components : — 

First. The component acting in the direction of the current and 
expended in overcoming the ohmic resistance. This component is 
often termed “ The Power Electro-motive Force,” and is numerically 
equal to RI. 

Second. “ The Reactive Electro-motive Force ” in quadrature 
with the current, and employed in balancing the counter E.M.F. of 
inductance, and numerically equal to Lwl. 

420. Reactance. — The quantity Lob, which is the measure of 
this effect, has recently been denominated “ Reactance ” by the 
American Society of Electrical Engineers, and is defined as “numer¬ 
ically equal to the component of the impressed E.M.F. at right angles to 
the current , divided by the currentd The reactive E.M.F. in any cir¬ 
cuit may arise from inductance, mutual inductance, capacity, or from 
the introduction of a counter electro-motive force due to any exterior 
cause ; and the impressed E.M.F. may always be regarded as the 
vector sum of two components, one of which transmits power, and 
the other which balances “reactance.” In circuits containing mutual 
inductance, the reaction due to the current in the secondary coil may 
be resolved into two components, one in the same direction as the 
primary, and the other at right angles to it, thus obeying the fore¬ 
going definition. Some objection to this broad use of the term “ re¬ 
actance ” has been made by Continental electricians, who hold that 
the employment of words ending in “ ance ” should be restricted to 
apply to the constants of a circuit; thus resist ance, conduct#//^, per- 
mitt ance, are invariables for any given circuit ; while under the above 
definition, “ reactance ” would vary when applied to circuits contain¬ 
ing motors or mutual inductance. P'or such circuits all confusion 
may readily be avoided by using the term “ equivalent reactance,” or 
equivalent resistance in cases where such quantities can be variable. 

Reactance is measured in ohms. In many respects it closely 
resembles resistance, but no power is expended in overcoming react¬ 
ance, as it is at right angles to the current; and, therefore, the 
product of this E.M.F. component and the current is zero watts. 
As will presently be shown, reactance may arise from other influ¬ 
ences than simple inductance. From an inspection of the diagram, 



342 


THE ELECTRIG AL TRANSMISSION OF ENERGY. 


it will be seen that reactance tends to produce a phase difference 
between the impressed electro-motive force and the current. If 0 
represents this angle, 

Q _ ZC Reactance Zoo 

AB Resistance K 


the current being in advance of the impressed electro-motive force 
when 0 is positive, and lagging behind it when it is negative. 

421. Impedance. — The quantity NR 2 -f- L 1 go 2 , represented by 
the hypothenuse of the triangle, as the vector sum of the resistance 
and the reactance, has been termed “The Impedance of the Circuit,” 
denoting the total opposition to transfer experienced by the current. 
In a simple circuit containing only resistance and inductance, the 
power E.M.F. is equal to the ohmic E.M.F, or RT, and the reac¬ 
tive E.M.F. is equal to the inductive E.M.F., or ZcoZ This may 
be indicated in the diagram by simply changing the scale sufficiently 
to introduce the numerical factor Z. As an example, assume in the 

diagram, Fig. 210— — „ ... . 

& & AB = R = 40 ohms, 

BC = Z = .08 henry, 

n = 60, 


to = *> t ( 


then Z oo = 2 x 3.1415 X 60 x .08 = 30.16 = BC, and the impe¬ 
dance AC equals V40 2 -f 30.16 2 = 50.095 ohms, say 50 ohms. With 
a maximum impressed E.M.F. of 1000 volts the maximum current 
will be = 20 amperes. The power E.M.F. = 40 x 20 = 800 

volts. The reactive E.M.F. = 20 x 30.16 = 600 volts, while the 
current will lag behind the impressed E.M.F. by an angle whose 
tangent is ? 0,lg . = .755, or 37°. The arrows indicate the direction 

0 4 0 

of the forces. 


Sec. a. — The Resistance Variable. 

422. Suppose that in any given circuit E and Z remain constant, 
while R becomes variable, what is the effect on Z? With a continuous 
current, Z varies directly as R ; but in an alternating current circuit, I 
varies as the vector sum R and Zw, or as VZ 2 -f- ZV. From in¬ 
spection, it is evident that when R = 0, I = E / Zoo. Therefore, 
when R vanishes, the current can never attain a greater value than 
E / Zoo. When R = 00 , Z becomes 0 ; thus these values indicate the 









CONDUCTORS FOR ALTERNATING CURRENTS. 


348 


limit of / in both directions. To determine the successive values of 
/ between these boundaries, construct a triangle of energy, as shown 
in big. t? 11, “ Diagram of Current Values in Circuits containing Re¬ 
sistance and Inductance with Variable Resistance,” by drawing AB 
positively and equal to Rf t BC perpendicularly to AB positively and 



F 

Fig. 211. Diagram of Current Values in Circuits containing Resistance and Inductance with Variable 

Resistance. 


equal to Lwf, then AC = / x s/R‘ + Z, 2 « 2 . Divide RI by R to find 
the value of I. Suppose this to be AD, then by similar triangles — 


DE = 


Lw/ 



and 


AE = / X 


VA 2 + ZW 
R 


423. The maximum value of / is E j Lm ; and when the current 
has this value, the power component of the impressed E.M.F is 0, 
and the current is 90° behind the impressed E.M.F. When R is 
infinitely large, the current is infinitely small, the angle of lag 



















344 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


becomes infinitely small, and the vanishing current coincides with 
the impressed E.M.F From A draw AF perpendicularly to 
AC == E / Lo). By its magnitude and direction, this line represents 
the maximum value of the current. Also the point A represents in 
direction and magnitude the vanishing value of the current, and coin¬ 
ciding with AC represents the minimum value of the current. All 
other values must lie between these two. On AF as a diameter, 
draw a semicircle AGF. By geometry, all triangles drawn as ADF 
on AF, and limited by the semicircle AGF, are right-angled at D ; 
but the maximum and minimum limits of these triangles are the 
maximum and minimum limits of the current values, hence all cur¬ 
rent values may be represented by the varying values of the vector 
AD. 1 As a concrete example, assume — 


R 

I 

n 

L 


then, 


4 amperes, 
50, 

.004 henry, 


0 ) 

Zm 

RJ 

Em/ 


314.15, 

1.25, 

10 , 


= o : 


e = i = 4 V2J5M_~'i Eg 2 = i i.is. 

A 
R 


11.18 


2.5 


= 4.47 


E 11.18 Qnr RI 10 

: -=- = o.y*_> ; -= - 

Zw 1.25 Zw 1.25 


= 8 . 


tan. 0 


L eL = 1^1 = A = .5 = 26° 34' 

RI R 10 

90° — 0 = 63° 26'. 


Sec. b. — Inductance Variable. 

424. When L varies, the current limits are 0 when L is infinity, 
and E/ R when L is 0, the current equation then reducing to Ohm’s 
formula. By a similar train of reasoning to that employed in Sec. a } 
it is easily shown that when L is variable, the current variation is 
given by a vector drawn from point E in the previously mentioned 
diagram, and limited by a semicircle drawn on AE. This is indi¬ 
cated in the illustration by dotted lines. The arrows indicate the 
direction of the current variation in both Secs, a and b. 

425. 3. Electrical Properties of Simple Circuits with Several 
Resistances and Inductances in Series. — In the case of a circuit 
containing a number of distributed resistances and inductances, the 

1 This proposition was first demonstrated by Messrs. Bedell and Crehore, see Alternating 
Currents, p. 223. 















CONDUCTORS FOR ALTERNATING CURRENTS. 


345 


impedance is calculated by obtaining the vector sum of all resistances 
and the sum of all inductances. This is most conveniently done 
diagrammatically, as indicated in Fig. 212, “ Diagram of E.M.F in a 
Circuit containing Several Resistances and Inductances in Series.” 
1 here are two methods, each attaining the same result, though the 
first to be described has the advantage of more clearly featuring all 
points of the circuit, and indicating more explicitly the distribution 
of currents and potentials. Assume as an example a 
circuit having the following properties : — 


R 

= 6 ohms, 

eo 

= 1885, 

Leo 

= 4.52, 

R r 

= 3 ohms, 

L 

= .0024, 

Leo 

= 8.29, 

R" 

= 9 ohms, 

r 

= .0044, 

L"eo 

= 10.00. 

ii 

= 30. 

L" 

= .0053, 




Lay off ab 

= 6. 

From b 

draw bb' 

per- 


pendicularly and positively, and lay off 
bli = Leo = 4.52. Draw ab ', which 
will be equal to 

V R 1 + Z 2 0) 2 = V6 2 + 4.52 2 = 7.51 =/, 

the impedance of R and Leo. 

From b' draw b'c parallel to 
&b, and make it equal to 
R 1 3. From Fdraw c c" 
parallel to bb\ and lay 
off 7T 7 = Leo = 8.29. 

Draw 


j ji 


be 
equals — 


then b'c" 



V R' 2 + Z'V 2 = V3 2 + 8.29 5 
= 8.82=/'. 


Fig. 212. 

Diagram of E.M.F.s in a Circuit Containing Several Resistances 
and Inductances in Series. 


the impedance of R' and L eo. 

Proceed in a like manner with R" and L"eo, obtaining point e, 
then c" e will be the impedance of R" and L"m, or J" = 13.45. Join 
a and e. Then ae will represent J v = 29.05, the impedance equiva¬ 
lent to the vector sum of all resistances and all inductances. The^ 
same result may be gained as shown by the dotted lines, by which the 
sum of R + R' + R ",is laid off horizontally, positively, as ab-]- bc-\-cd, 
then the sum of Leo + Leo -p L" eo is laid off vertically, positively, as 




















346 TIIE ELECTRICAL TRANSMISSION OE ENERGY. 

db" -f b"d' + d'e, thus reaching the same point e as in the previous 
construction, obtaining J n = 29.05, as before. The angles of lag of 
the current, and the components of the E.M.F, are calculated in the 
manner already indicated. By the latter method, the total impedance 
of the circuit obtained is the same as that given by the former ; and 
while more speedy of execution, the former gives a much clearer and 
more vivid idea of the component parts of the circuit. 

426. 4. Electrical Properties of Simple Circuits with one 
Resistance and one Capacity in Series. — Turning to big. 207, and 
remembering that the tangent to the current curve KRMSO has a 
maximum value at the points O and 7 r, it is evident that at these 
points there will be the greatest difference of potential exerted on 
the capacity of the circuit, and a maximum current will flow. It is 
also evident that the condenser current will oppose the line current ; 
for as the current in the line decreases, the charge in the condenser 
will flow out, tending to continue the line current by the amount of 
charge due to the capacity, while, when the current is increasing, 
the condenser will absorb electricity, thus tending to reduce the 
line flow. 

427. As an aid to the conception of the role played by a con¬ 
denser, and its effect to introduce an E.M.F. 90° in advance of the 
impressed E.M.F ., consider the mechanical analogy of the common 
hydraulic elevator supplied with an air compression tank. The ele¬ 
vator is operated by a piston traveling to and fro in a cylinder. As 
the elevator falls, water is forced into the tank, and the air com¬ 
pressed ; while, as it rises, the pressure of the compressed air tends 
to balance the weight of the car. To stretch the analogy a little, 
suppose the elevator to make regular trips, thus moving harmonically, 
and suppose that when it is at mid-stroke, the air in the tank is at 
atmospheric pressure. The motion of the elevator will be swiftest 
at mid-stroke and zero at either end, and may typify the current 
curve; the top, middle, and end of the stroke corresponding to the 
points 7 r / 2, 7 r, and o 7 r j 2, of Fig. 207. The counter E.M.F. set up 
by the condenser has its analogy in the air pressure in the tank, while 
the charge is represented by the amount of water forced in. When 
the car is at mid-stroke, it is moving most rapidly, the air pressure 
is zero, and the water occupies one-half the space devoted to it in the 
tank. This state corresponds to the points O and tt in Fig. 207. 


CONDUCTORS FOR ALTERNATING CURRENTS. 


347 


Power E.M.F. R I 


As the car falls, the water is forced into the tank, the air pressure 
increases, the tank is filled, and the motion of the car decreases to 
zero ; corresponding to a quarter period on the curve from O to f. 
At the points O and -n the charge and counter E.M.F. are zero, and 
the current is a maximum. Between O and -n / 2 the current de¬ 
creases ; the charge and counter E.M.F. increase. From mid-stroke 
to the end the increasing air pressure opposes the fall of the car, 
as the increasing counter 
E.M.F. opposes the cur¬ 
rent, while the increasing 
volume of water typifies 
the augmenting condenser 
charge. As the air pressure 
balances the car, it is evi¬ 
dently equal, and opposite to it, 
and must be 90° in advance. The 
effect, therefore, of the condenser 
is to introduce an E.M.F. 90° in ad¬ 
vance of the impressed E. M. F. This 
condition is indicated in the diagram by 
the broken line III or VWYZ. The same 
relation is shown algebraically in the solution 
of the General Energy Equations. Thus, Ca¬ 
pacity introduces a Reactance measured by 

Remembering the negative nature of this Reactance, 
the triangle of E. M. E. may be constructed vectorially, 
as already indicated in the sections applying to Resist¬ 
ance and Impedance. 

428. In Fig. 213, “ Diagram of Electro-Motive Force in a Sim¬ 
ple Circuit containing Resistance and Capacity in Series,” draw 
AC horizontally and positively equal to R. From C draw BC nega¬ 
tively, and to the same scale equal to the quantity —. Draw 



C 


AB, then AB represents \ R 2 + CM 1 ' Adopting a sail ^ ar notation to 

that employed in the diagram of electro-motive force in a simple 
circuit containing resistance and inductance in series, the horizontal 








348 


THE ELECTA'/CAL TRANSMISS/OH OF ENERGY. 


line AC measures the resistance of the circuit, and by a simple change 
in scale, to introduce the factor /, will measure that component of 
the impressed electro-motive force which is in phase with the current, 
usually denominated “ Power Component." The line BC measures 

the reactance- , or the reactive component of the impressed elec- 


_ / ■ i 

tro-motive force —Ij Cm ; while AB measures the \j R 2 -f- 2 , and 

’ 6 “or 

is the impedance of the circuit. When the factor / is introduced in 
the two sides of the triangle, the hypothenuse measures the total 
energy of the circuit El. To illustrate by a concrete example. Sup¬ 
pose in the diagram the same value for the resistance R , 40 ohms, 
and 7 / = 60 as was assumed in the diagram of electro-motive force in 
a simple circuit containing resistance and inductance, then co = 377. 

Let C equal .00000425 farad, then — -i— == — 62.6 and \j R 2 -f- —„ 

Cm ' C “or 


= V40 2 -f- 62.6 2 = 74.3 ohms. The properties of impedance and 
reactance, as given in this diagram, are similar to those described in 
the section treating of resistance and inductance in series ; namely, 
the impedance of the circuit is the effective resistance or opposition 
encountered by the current, and which, when substituted for R in 
Ohm’s law, renders his formula equally applicable to the alternating 
current circuits. The reactance of the circuit also possesses the 
same properties as indicated in the previous example; remembering, 
however, that the effect of inductance is to introduce a positive 
reactance, while the effect of capacity is to introduce one which is 
negative. Thus, it is apparent that capacity tends to oppose and 
neutralize inductance, and by proper proportioning of these quantities 
in any circuit, one may be so designed as to counteract and neutralize 
the other. 

Sec. a. — Resistance Variable. 

Sec. b. — Capacity Variable. 


429. In the paragraph treating of electrical properties of 
simple circuits with one resistance and one inductance in series, 
two sub-headings were given, indicating a method of geometrical 
construction whereby the different values of the current could be 
ascertained when either the resistance or the inductance in the 
circuit was supposed to vary from zero to infinity. As capacity has 











CONDUCTORS FOR ALTERNATING CURRENTS. 


349 


A 


A 


been shown to introduce a negative reactance in the circuit, it is 
evident that the same construction may be used to determine the 
varying current in a circuit containing resistance and capacity, by 
.constructing a diagram precisely similar to the one already alluded 
to, in which the reactance of the circuit is laid off nega- 
lively instead of positively; thus, under these circum¬ 
stances, in a circuit containing resistance and capacity, 
when these quantities vary from zero to infinity, varying 
values of the current will be found as vector quantities 
bounded by semicircles drawn upon diameters having the 
values of E / 1 / Cm when R is variable, and upon a di- 

JNEU + 1 / cv 


“f - 

1 

3 


ameter equal to 


R 


when C is variable. 




O 

§1 


In a construction so 
obvious it is not ne¬ 
cessary to repeat the , 
diagram. ^ 

430. 5. Electrical 
Properties of Simple 
Circuits with Several 
Resistances and Ca¬ 
pacities in Series. — 

In the case of a num¬ 
ber of resistances and 
capacities in series, 

the diagram of electio- ^ 274. Diagram of a Simple Circuit containing 

motive force mav be Resistance, Inductance, and Capacity 

J in Series. 

constructed as indi¬ 
cated in No. 3, bearing in mind the negative value of the reactances, 
and drawing the vectors representing them negatively downwards. 
In every other particular the construction is precisely the same 
as that outlined in No. 3, and the result may be obtained by the 
directions there given. 

431. 6. Electrical Properties of Simple Circuits with Resist¬ 
ance, Inductance, and Capacity in Series. — To treat this case, it 
is requisite to recollect that the reactance of the circuit must be the 
vector sum of the positive and negative values of the two reactances 
developed by the inductance and the capacity. The case is ill us- 

















850 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


trated in Fig. 214, “ Diagram of Electro-Motive Force in a Simple 
Circuit containing Resistance, Inductance, and Capacity in Series,” 
by assuming the values given in the previous examples, Nos. 2 and 
4, namely : — 

R = 40, Zw = 30.16, 

TV = 60, 1 / Cm = 62.6, 

C = .0000425, w = 377. 


From any point B, draw BD perpendicularly and positively equal 
to Lm = 30.16. From D draw DC negatively downwards equal to 
— 1 / Cm. For a certain distance DC will coincide with DB, but 
as 1 / Cm is greater than Aa>, CD will be longer than DB. The 


difference, BC, will be equal to the vector sum of Lm — 
_ 62.6 = - 32.44. 


T = 30.16 

C M 


From B draw BA horizontally and equal to A 5 , in this case equal 

to40. Draw AC, then the vector AC is equal toy A'- -f (^Lm -. 

In this diagram, as it is constructed, the vector sum of the three 


quantities R -f Lm -—- has been obtained, which is evidently 

the impedance of the circuit in question. As in the previous dia¬ 
grams, the horizontal line AB represents the resistance, or by a 
change of scale sufficient to introduce the factor /, represents the 
power component of the impressed electro-motive force. The ver¬ 
tical line BC represents the net reactance of the circuit, or the 
vector sum of the positive reactance due to impedance and negative 
reactance due to capacity ; while AC represents the impedance of 
the circuit, or the impressed E.M.F. when the factor / is intro¬ 
duced. 

432. 7. Electrical Properties of a Simple Circuit with Sev¬ 
eral Resistances, Inductances, and Capacities in Series. — By 
the principles already laid down, it is evident that where a number 
of resistances, inductances, and capacities are joined in series in a 
single circuit, the solution of the problem may be directly obtained 
by constructing an appropriate triangle of electro-motive forces, giving 
the vector sums of all the quantities producing impedance. Either 
of the methods given in- No. 8 may be used, care being taken 








CONDUCTORS FOR ALTERNATING CURRENTS. 


351 


to attribute to each vector its appropriate direction, positively and 
negatively. 

433. 8. Electrical Properties of Circuits with Resistances, 
Inductances, and Capacities in Multiple Arc. — In the previous 
chapter it has been shown that in the case of a continuous current, 
the total resistance of a number of branch circuits joined in multiple 
arc is given by the reciprocal of the sum of the reciprocals of all 
the resistances. It has been shown that Ohm’s formula applies to 
alternating current circuits when the apparent resistance or im¬ 
pedance of the circuit is substituted for R in the ordinary formula ; 
so, in the case of alternating currents when traversing circuits in 
multiple arc, if for R the impedance of the various circuits be 
substituted, a correct solution is immediately arrived at. Therefore 
if, in accordance with the principles already laid down, the im¬ 
pedances of a number of multiple arc circuits be determined, and the 
sum of the reciprocals of these impedances be obtained, the total 
impedance of the circuit will be the reciprocal of this sum. To J illus¬ 
trate the case by a concrete'diagram, suppose in Fig. 215, “Diagram 
of Electro-Motive Forces in a Complex Circuit containing Several 
Resistances, Inductances, and Capacities in Parallel,” that G repre¬ 
sents the diagram of the circuit. Here X is the generator to which 
five circuits, A, B, C, D, and E are joined in multiple arc. The 
circuit A has a simple resistance of 60 ohms ; the circuit B has a 
resistance of 30 ohms in series with an inductance of .06 henry ; the 
circuit C has a simple capacity of 13 mf. ; the circuit D has a resist¬ 
ance of 50 ohms in series with a capacity of 5 mf., and an induct¬ 
ance of .18 henrys. The circuit E has a simple inductance of .09 
henrys. To determine the total inductance of the circuit, assume 
any base line as ax. On this base line lay off ab equal to R, equal 
to 60. As there is no inductance, the impedance in this circuit 


Ja = CO. 


At any other point on the base line, construct a triangle of the 
electro-motive forces for the second circuit B, by laying off cd = R = 
30 ; dc vertically and positively = Leo = 45.24. Join ce to obtain 
the impedence J B = 54.27. Proceed in a like manner with the 
remaining circuits, C, D, and E, obtaining the inductances — 


J v = 102.02, 




1 The frequency n in this example is 120 per second. 


352 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 






X 

*0 


0 




Fig. 215. Diagram of E.M.F.s in a Complex Circuit with Several Resistances, Inductances, and Capacities in Paralle 


























CONDUCTORS FOR ALTERNATING CURRENTS. 


353 


Each of these are plain vectors. Obtain now the reciprocal of each 
one, remembering that the reciprocal of a vector is a plain vector 
having a scalar magnitude equal to the reciprocal of the original 
vector and lying in the same direction. Thus, — 

the reciprocal of J A = .0166, the reciprocal of J D = .0072. 

J B = .0183, J E = .0148. 

J c = .0098, 

Assume any point, a', and draw a'b' parallel to ab, and make it 
to any convenient scale equal to the reciprocal J A . 

From b' draw b'e parallel to ce, making b'e' equal to the reciprocal 
J B . From e ' draw e'g' parallel to fg, making e'g' equal to the recip¬ 
rocal of fg. From g' draw g'j', parallel to kj, making it equal to 
the reciprocal of J D . From j' draw j'i' parallel to ml, making it 
equal to the reciprocal of J E . Join the points, a ' and i\ then the 
line a'i' will, in direction, represent the resultant electro-motive force 
acting in the circuit, and in magnitude will be the sum of the recipro¬ 
cals of all the impedances in circuit. Obtaining the reciprocal of 
this sum, in this particular case equal to 30.5, the total impedance 
of the circuit is given as 30.5 ohms. 

The phase of the impressed electro-motive force, with reference 
to the currents in the various branches or parts of the branches, 
may be found by the previously given rules. The direction of the 
arrows in the diagram indicates the direction of the current in the 
various parts of the circuit. 

434. Method of Equivalent Resistance and Inductance. —- 
When a number of circuits in multiple arc are acted upon by an 
electro-motive force, it is possible, theoretically, to replace the several 
resistances, inductances, and capacities, by an equivalent resistance 
and inductance, remembering that a capacity is equivalent to a nega¬ 
tive inductance. The equivalent resistance and inductance would be 
such a resistance and inductance as would cause the same current 
(both in magnitude and phase) to flow in the main leads, as would 
pass when the several parallel circuits were connected. The substi¬ 
tution of such an equivalent inductance and resistance evidently 
produces no change in the main circuit, and could displace the 
branch circuits without producing any variation, either in magnitude 
or in phase, in the original current. The employment of such a 









354 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


hypothetical substitution as this simplifies, in some cases, the solu¬ 
tion of problems in alternating currents, when applied to a number 
of branch circuits. The application of this method is a direct cor- 


A 



A' 



Fig. 216. Diagram of the Method of Equivalent Resistance and Inductance. 


ollary to the proposition of Art. 422, and can be, perhaps, most 
clearly described by the use of an example. Suppose in Fig. 216 
the generator G supplies two leads A and A', extending from the 
generator to a center of distribution. From this point suppose four 



















CONDUCTORS FOR ALTERNATING CURRENTS. 


355 


circuits B, C, D, and E to be placed in parallel across the leads, and 
let each circuit be respectively denominated by its appropriate letter. 
Let the frequency be 159.15, so that = 1000. For the circuit B : — 

= 3 ohms, L B = .002 henry, L b m = 2. 

For the circuit C : — 

jR c = 1.5 ohms, L c = .0043 henry, L c w = 4.3. 

For the circuit D : — 

R d = 2.5 ohms, C D — .00006 microfarad, C d m = .06, 1 / C D co — 16.67. 
For the circuit E : — 

R E = 1.5 ohms, C E = .00019 microfarad, C E co = .19, 1 / C E co = 5.26. 

From the above data the impedance of each branch circuit may 
be directly calculated, as, — 

J B = 3.60, J c = 4.56, J D = 16.72, J E = 5.47. 

Now, assume any convenient electro-motive force to act at the 
center of distribution, uniformly affecting all of the branch circuits. 
For this purpose it is very convenient to assume 100 volts, as then 
all the quantities to be derived from the solution will be in percent¬ 
age, and may be conveniently and easily handled. With the assump¬ 
tion of 100 volts as the electro-motive force, calculate from the 
impedance as above obtained, the currents in each of the branches, 
obtaining, — 

I B = 27.8, I c = 21.9, f D = 5.98, I E = 18.2. 

Now, referring to the diagram, draw any line AB to any con¬ 
venient scale, making AB equal to 100 volts. At A lay off Ac, 

making the angle BA<: equal to tan -1 ^^. If the line AB represents 

Rb 

the electro-motive force, then the line Ac is equal to I B R B , and the 
line cB is equal to L b mI b . In a similar manner construct other tri¬ 
angles AeB, A^B, and AhB, remembering that in circuits containing 
inductance the angle 0 must be laid off from the line of electro-motive 
force negatively, while in circuits containing capacity it must be laid 
off positively. From what has previously been demonstrated, it is 
obvious that the points e, c, B, h, g, and A will lie on the circumfer¬ 
ence of a circle drawn upon AB as a diameter. On each of the 
lines Ac, Ae, Ag, and Ah, lay off Ad, A/, Ah, and At, respectively, 













356 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


equal to the currents in each of the branches, or in other words, 
divide these lines by the resistance in each branch. The lines Ad, 
A f, Ak, and A i, will then represent, in direction and magnitude, the 
currents in each of the branch circuits. From what has previously 
been shown, it is evident that the vector sum of all the currents 
would be equivalent to the resultant current, or the current in the 
main lines A, A'. To obtain this resultant current select in the dia¬ 
gram any current vector as A f From the point f draw a line 
parallel to the next current vector Ad, and lay off fb equal to Ad. 
From the point b draw bin parallel and equal to A i. From the point 
m draw inn equal to Ak. The broken line Afbmn represents the vec¬ 
tor addition of all the lines representing the currents, or in other 
words, forms a polygon of currents. This construction is parallel to 
the polygon of forces in mechanics. To find the resultant current, 
namely, the vector sum of all the component currents, draw nA, thus 
completing the current polygon. Then the line nA will represent, 
both in direction and magnitude, the current in the main leads. 
Prolong nA until it intersects the circumference drawn upon the line 
AB at O. Then, evidently, the lines AO and OB represent respec¬ 
tively the product of the current in the main leads by such resistance 
and such inductance as is equivalent to the vector sum of all the 
inductances acting in the branch circuits, or AO = RI A and OB = 
LoJ a . By dividing these lines by the current, the respective desired 
equivalent resistance and inductance is immediately obtained. In 
this particular example the current in the main leads,—• 

I A — 39.4, RI a — 94.3 R = 2.37 = equivalent resistance. 

Lm/ a = 33, Zco = .838, Zoo / oj = .000838 = equivalent inductance.. 

The tangent of the angle of lag is obtained in the usual manner. 

435. By this method the currents in each of the branch circuits,, 
and the equivalent resistance and inductance necessary to produce in 
the main leads the same current as would flow with all of the parallel 
circuits working under the given conditions, are obtained. The as¬ 
sumption, however, has been made of an electro-motive force of one 
hundred volts. If, now, any other electro-motive force is operative, 
it is simply necessary to change the scale of the entire diagram by 
the proportion which 100 bears to the real electro-motive force. To 
complete the solution of the problem, it must be recollected that so 

















CONDUCTORS FOR ALTERNATING CURRENTS. 


357 


far no account has been taken of the circuit AA', extending from the 
generator to the “ Center of Distribution.” The entire solution of 
the problem is evidently obtained by taking the vector sum of the 
resistance and inductance of the main leads, together with the 
equivalent inductance and resistance of the branch circuits, as given 



by this problem. The method of obtaining the vector sum of two 
inductances and resistances in series has already been given. 

436. 9. The Properties of Circuits containing Mutual Induc¬ 
tance. — The most frequent and important cases of mutual inductance 
are to be found in the construction of dynamo machinery; the com¬ 
mon transformer forming a convenient example. Here two circuits 
are in close proximity to each other, in one of which an impressed 
















358 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


E.M.F. acts, producing by mutual inductance a useful E.M.F in the 
neighboring circuit. Mr. Kennedy 1 is the deviser of the neatest 
method of graphically solving this problem, of which the following 
example is an illustration. 

Assume two circuits A and B, indicated in Fig. 217, “ Diagram of 
E.M.F. in Mutually Inductive Circuits.” For simplicity, a non-mag- 
netic medium is predicated ; though by the simple introduction of the 
permeability factor ^ in the formulas, the same treatment will apply 
to any media. Suppose the circuit A to consist of a generator sup¬ 
plying an E.M.F. denoted by E a = 1000 volts. Let the resistance 
and inductance of the generator be respectively r al = 5 ohms, and 
4i = .02 hen. Let the line have a resistance of r a2 — 10 ohms, 
and an inductance of l a2 = .01 hen., with a capacity of C a = 15 mf. 
Let the resistance and inductance of the primary coil be r a3 = 40 ohms, 
and l a3 = .12 hen. Then the total resistance R a = r al + r a2 + r a% 
= 5 + 10 -f- 40 = 55 ohms, and the total inductance L a — 4i + 42 
+ 43 = .02 -f- .01 -j- .12 = .15 hen. For the secondary circuit, sup¬ 
pose the resistance and inductance of the coil to be r bl = 15 ohms, 
and l bl = .18 hen., and for the leads r b2 = 10 ohms, and l b2 = .015 hen., 
with a capacity of C b = 8 mf. ; with finally a resistance and inductance 
in the receivers of r b3 = 100 ohms, and l b3 = .005 hen. Then the 
total resistance and inductance of the B circuit is R b = r bl -f- i' b2 
+ r b3 = 15 + 10 + 100 = 125 ohms, and L b = l bl -f l b2 + l b3 = .18 
+ .015 + .005 = .20 hen. Let the mutual inductance be M = .12 
hen., and the frequency 159.15 (in round numbers 160), so that 
oo = 2 7r 72 = 2 X 3.14 X 159.15 = 1000. 

437. As a preliminary to the final solution, suppose the circuit 
B to be absent, then in circuit A the impedance — 



— V55 2 -j- 83.4 2 


99.9 ohms. 


Denote the reactance of circuit A, f L aM -= 83.4, by p a . The 

V Ca**] 

current in circuit A is i a = E a JJ a = 1000 / 99.9 = 10 amperes 
(about). The triangle of E.M.F. is drawn as at C by laying off from 
A AB = R a = 55 ohms. From B draw BC perpendicularly and 
positively equal to L aM = 150. From C lay off CD perpendicularly 


1 Electrical World , vol. xxii., p. 306. 







CONDUCTORS FOR ALTERNATING CURRENTS. 


359 


and negatively equal to = 66.6, thus leaving DB = p a = 83.4. 


Draw AD, obtaining_/ rt = 99.9. 

438. Now suppose circuit B to be brought into such relations 
with circuit A that the coefficient of mutual induction M shall have 
the previously assigned value of .12 hen. The first effect of the cur¬ 
rent i a in circuit A is to initiate an induced E.M.F. in circuit B 
measured by co Mi a = E b = 1000 x .12 x 10 = 1200 volts ; tend¬ 
ing to produce in B a current i b = E b jJ b . But — 



Also 



and hence 


1200 Q0 j 

tb = TTEq = am P 6res - 

140.0 


Construct now the triangle of E.M.F. in the secondary circuit B, as 
shown at D by the methods already given. The current in the cir¬ 
cuit B will react in turn on A, tending in that circuit to set up an 
E.M.F. that would give rise to a current superimposed on the current 
i a that is already passing. The modified primary current will again 
react on the secondary, causing a new adjustment of current value, 
this process continuing till equilibrium is attained. Denoting by i A 
the final value of the current in the A circuit, this value could be 
derived from the expression i A = E a /J A , in which J A is different 
from J a . The value J A of the impedance, which will give the true 
amount of the final current in the A circuit, may be termed the 
“ Effective Impedance ; ” and is shown to be derived by increasing 
the resistance of the A circuit by a quantity z 2 R b , and diminishing 
the reactance by z 2 p b ; in which z = co M/ J b . The final primary cur¬ 
rent then becomes — 


V(^a + Z 2 E b y 4- (p a — Z 2 p b y 

In this example, z = 1000 x .12 /145.8 = .828 ; z 2 R h = 85.5 ; 


(175) 


and z 2 p b = 51.5 ; therefore, 


1000 


V(55 + S5.5) 2 + (83.4 - 51.5) a 


7 amperes. 
















360 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


It also follows that the true secondary E.M.F. will be equal to 
o oMi A = 1000 x .12 x T = 840 volts, and the current in the circuit 
B = z B = E b // b = zi A = 840 /145.8 = 5.8 amperes. This result is 
graphically shown at C by increasing AB to AE, making AE = z 2 E b ; 
and decreasing BD by ED = z 2 p 0 . Then the effective impedance J A 
is FE = 143.6. The angles of phase may be determined in the 
usual manner. 

439. In this example, only one of the circuits has been given an 
impressed E.M.F. ; but the same method can readily be extended to 
embrace an impressed E.M.F. in both circuits, by taking in circuit B 
the vector sum of the impressed and induced E.M.F. No allowance 
is made for hysteresis, which will doubtless limit to a certain extent 
this method. 

440. Impedance Tables. — From the preceding considerations, 
it is perceived that inductance and capacity, when of sensible amount, 
play an exceedingly important part in modifying the current, both in 
magnitude and direction. For convenience in treatment, the subject 
may be divided into two parts : — 

Case I. — Circuit containing Resistance and Inductance. 

Sec. a. Two parallel aerial wires as a complete metallic circuit. 

Sec. b. One aerial wire with ground return. 

Sec. c. Concentric cables. 

Case II. — Circuits containing Resistance, Inductance, 

and Capacity. 

Secs, a , b, and c , as above. 

Sec. d. Effect of adjacent bodies. 

Case I. — Circuits containing Resistance and Inductance. 

441. Sec. c. — Two parallel overhead wires, as a complete me¬ 
tallic circuit. 

From the energy equation the general value of the impedance J 
in any circuit containing resistance and inductance is VA 2 + E 1 o?. 
If, in this expression, R be the value of the ohmic resistance 
for a unit of length of the conductor, the value of J may be 
arranged as a simple numerical factor, to be used as a multiplier; 
and if l be the length of any circuit, R its resistance per unit 










CONDUCTORS FOR ALTERNATING CURRENTS. 


361 


of length, and J the impedance factor, the total impedance of the cir¬ 
cuit becomes JRl. The values of J may be determined graphically, 
with sufficient accuracy for common practice, by the aid of the ac¬ 
companying tables, with the avoidance of much tedious calculation. 
As the tabular values are given for commercial copper, it is only 
necessary, when the impedance factor is ascertained, to multiply it by 
the resistance of one unit length of the proposed conductor, and 
by the length of the circuit, to determine the total impedance. 

442. The coefficient of inductance L for two indefinitely long 

parallel wires is given on p. 328, as .5 + 2 log, -, where L is the 

r 

value per centimeter of length, when d is the distance between the 
centers of the conductors, and r the radius of the wire, in the same 
units. For demonstrations of this formula, the reader is referred to 
Mr. Kennedy’s paper on Impedance. 1 The resistance of the con¬ 
ductor per centimeter, when p is the specific resistance, is R = p / ?rr 2 . 
Substituting these values in the general expression for impedance, — 



By inspection, this expression is resolvable into four parts ; viz. : — 




.4 


and 


r 


Each of these parts, or components, may be plotted as a curve, and 
the value of the entire quantity obtained rapidly by summing the 
separate parts. It is the object of Table No. 44 to facilitate this 
process. 

443. The base line of the portion of Sheet 1, on the right of the 
double line, is divided into 100 equal parts allotted to the diameter 
of the conductor. The top of the sheet is similarly allotted to the 
distance between the axes of the conductors. As the scales are deci¬ 
mal, either, or both, may be multiplied or divided by any power of 10, 
in order to extend the range of the Table. The vertical axis in the 
center of Sheet 1 gives the values of d / r. Thus, the portion of 
Sheet 1 marked a, bounded by the top and bottom lines of the sheet, 
the vertical axis on the left, and including the diagonals to the equal 
part scale on the base line, will give the value of d/ r for a circuit of 


1 Trans. A. I. E. E. ; vol. x., No. 4., p. 203. 







362 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


any size of wire from .001" to 1" in diameter, and having the axes 
of the conductors separated from .1" to 100" apart. 

444. On the left hand of the double line, the curve b on Sheet 1 

gives the values of (.5 -f- 2 log, , the vertical axis and scale for 

this curve being the same as that for d / r. On Sheet 2, curve d on 
the left hand of the sheet is an extension to higher ranges of the 

( d\ 2 

curve b of Sheet 1, giving extended values of ( .5 + 2 log, - J . The 

curve c, Sheet 1, gives on the extreme right-hand scale the values of 
r 4 in the same units as the base line of the sheet; so if the base line 
be multiplied or divided by any power of 10, this axis must be simi¬ 
larly multiplied or divided by the same power of 10 raised to the 
fourth pozver. 

On the right hand of Sheet 2 is the frequency curve e, giving the 
value of 47r 4 /2 2 / p 2 . 

445. An example will illustrate the use of the tables. Let it be 
required to find the impedance factor of two parallel wires, No. 18 
Am. W. G., one-half inch apart, working under a frequency of 150. 
The dotted lines on the tables indicate the course to be followed in 
obtaining the components of the factor. The diameter of No. 18 
wire is 40 mils. On Sheet 1 find the diagonal ending at 40. Fol¬ 
low this diagonal until it intersects a vertical line passing through .5 
of an inch, on the top base line for the distance separating the wires. 
In this case, the vertical through .5 in. does not intersect the diagonal 
through 40 ; therefore, take the vertical through .05, or, in other 
words, divide the distance between the wires by 10. From the point 
where the vertical through .05 intersects the diagonal through 40, 
follow a horizontal line to the left, finding in the column marked 
“ Values of d / r” the quantity 2.45. As the upper base line used as 
the distance between the wires was divided by 10, the value found 
for dI r must be multiplied by 10, making 24.5 for the value of d/ r, 
thus determining one of the desired components of the impedance 

factor. As the curve b for values of ^.5 + 2 log, on Sheet 1 

does not run as high as 24.5, turn to the extension of the same curve 
d on Sheet 2. Find 24.5 on the scale marked d/ r ; follow a horizon¬ 
tal from this value to the left, to the intersection of the curve. From 


CONDUCTORS FOR ALTERNATING CURRENTS. 


363 


this point follow the vertical line downward to the base line, finding 
48 as the value of ^.5 -j- 2 log f < -\ , corresponding to d / r= 24.5, giv¬ 
ing the second component. To find the value of r 4 , return to the diag¬ 
onal ending in 40 on Sheet 1. From the foot of the diagonal, follow 
a vertical upward to the intersection with curve c, then follow a hori¬ 
zontal to the right to the vertical axis marked “Values of r 4 ,” finding 
.000006 as the value of r 4 , the third component. To ascertain the 
value of 4 7 rV 2 /p 2 , turn to the frequency curve e in Sheet 2, find 
the frequency (150 in this example) on the vertical axis on the right; 
follow a horizontal to the intersection with the curve, and then a ver¬ 
tical down to the base line, obtaining the value of 4 7 r 4 ;z 2 / p 2 as 3.1 for 
the fourth component. 

446. To recapitulate, the four components now stand : — 


then, 


1 st. 

4 t r 4 /r _ 3 ^ 

2 d. 

e 

3d. 

- = 24.5, 
r 

4th. 


V = .000006, 

(.5 + 2 log, ;)=48; 


/ = Vl + [3.1 X .000006 X 48] , 
/= VI.0008928, 

J = 1.000446. 


447. When the decimal paid of the quantity under the radical 
sign is less than . 1 , the square root may be found with sufficient 
accuracy by dividing the decimal part of the quantity by 2 , and pre¬ 
fixing 1 to the quotient. For greater values than this, consult any 
good table of square roots. The value of J thus found is the value 
for one unit of length. To obtain the total impedance of any circuit, 
it is now necessary to multiply this factor by the resistance of the 
conductor per unit of length (to be obtained from any wire table), 
and by the length of circuit expressed in the same units. In all cir¬ 
cuits falling under this case, the value of /will be greater than unity, 
indicating that the effect of inductance is to increase the resistance. 
As J varies as d, it is evident that this factor may be materially re¬ 
duced by bringing the two conductors as close together as possible. 
With uninsulated aerial lines, the wires must be separated at least 
six inches, or more, to prevent crosses. In conduit lines, with care¬ 
ful construction, this distance may be greatly decreased, while in 





364 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


concentric cables, d may be reduced to a fraction of an inch. 1 he 
table may also be applied to determining the impedance of circuits 
carrying polyphase sine currents of equally effective intensity, pro¬ 
vided the component parts of the circuit are equally distant from 
each other. The assumption is also made that the current density 
is uniform throughout the entire conductor, and that the current 
waves penetrate equally throughout its entire mass. For currents 
of ordinary frequency, this supposition is essentially true, attention 
having been already directed to “ Skin Effect.” The determination 
of the impedance factor, by this method, is accurate only when the 
form of the current wave is a sine curve. Any departure from this 
form serves to increase the value of the impedance factor, and must 
be calculated from the particular shape of the wave employed. As 
the departure from the sine curve is most apparent in poor dynamo 
machinery working on a light load, and as transmission calculations 
are always made for full load with good machinery, the agreement 
of the current wave to the theoretical form is very close, the method 
may be regarded as practically accurate. 

448. Sec. b. — An aerial line with ground return. 

When a circuit is composed of one aerial wire placed at a 
height “h" above the ground, and the earth used as a return, 
Mr. Heaviside 1 has shown that by the method of “ Images ” the 
ground may be replaced by an imaginary wire situated at an inter- 
axial distance from the real wire equal to 2 h. Such a circuit imme¬ 
diately reduces to Case 1, by making “ d” in the formula equal to 
twice the height of the line above the ground. 

449. Sec. c. — Concentric cables. 

Suppose one conductor to be rolled out into a thin sheet and 
formed into a tube surrounding the other conductor, this forming 
a concentric cable, in which the same amount of metal is employed, 
and the distance from the central conductor to the surrounding ring 
is maintained, the same as in the case of two parallel wires. Evi¬ 
dently, the resistance of the circuit is unchanged, and, also, each 
element in the ring is at the same interaxial distance as in the origi¬ 
nal circuit. The geometrical relations of the currents of the two 
conductors are unaltered, and the impedance may be calculated by 
the preceding methods, by substituting for d, in the preceding nota- 

1 See Jour. Tel. Eng., vol., vii. p. 303. 



CONDUCTORS FOR ALTERNATING CURRENTS. 


365 


tion, the value r of the radius of the external conductor in the con¬ 
centric cable. 


Case II. — Circuits containing Resistance, Inductance, and 

Capacity. 


450. S ec. a. — Two parallel aerial wires as a complete metallic 
circuit. 

The determination of the impedance factor for circuits containing 
resistance and inductance has been shown to be a simple matter. 
While both inductance and capacity are always present in all forms 
of electrical apparatus, the capacity effect is usually much less appar¬ 
ent, and may be more safely neglected, than that presented by induc¬ 
tance. Moreover, in a single circuit, inductance always manifests 
itself in series with the rest of the circuit, either sensibly, concen¬ 
trated at a single point, as in the case of a very short line supplying 
transformers, or else distributed from point to point along the line, 
as exemplified in a pair of transmission mains. Contrariwise, capacity 
usually exhibits itself as a high resistance shunt , acting as a branch 
circuit between the conductors, and must therefore be treated by 
the law of divided circuits. Occasions arise, as in the construction 
of some forms of dynamo machinery and in certain telephone circuits, 
where a large amount of capacity in the shape of condensers is placed 
in series at one point, in the circuits. Such cases, however, do not 
fall within the scope of transmission problems as usually understood, 
and when encountered may be solved by direct application of the 


formula 




Consider the case of an aerial line. 


Here are two indefinitely long parallel conductors, each having a 
surface equal to the length of one-half the circuit multiplied by the 
circumference of the conductors, and separated by a stratum of air 
equal to the distance between the wires. Evidently this combination 
possesses all the characteristics of a condenser placed across the 
conductors. If, now, the circuit be supposed to be subdivided into 
a large number of equal parts, each of one linear unit in length, and 
each part on one conductor be conceived of as joined to the corre¬ 
sponding part on the other conductor by a condenser having a capacity 
equal to the capacity of the line per unit of length, the line may be 
represented as the sum of a great number of branch circuits, each 





366 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


containing a capacity equal to the capacity per unit of length. The 
total impedance of such a circuit is the reciprocal of the vector sum 
of all the reciprocals of the branches. Moreover, as even dry air is 
not a perfect dielectric, and as aerial circuits are rarely, if ever, im¬ 
mersed in even moderately dry air, there will also be a certain amount 
of leakage across the conductors per unit of length ; and thus the 
branch circuits along the conductor may be regarded as circuits hav¬ 
ing a capacity equal to the capacity per unit of length of the line, in 
series with a resistance equal to the insulation of the line per unit of 
length. The line may now be regarded as a number of branch cir¬ 
cuits, containing resistance, inductance, and capacity, and treated 
accordingly. The full and exact solution of this problem leads to the 
use of hyperbolic functions and complex algebraic quantities. There 
are three methods of approximation which avoid mathematical diffi¬ 
culties, and which may be quickly and rapidly applied. 

451. 1. When the line is not over three to five miles in length, 
the total capacity and leakage may be considered as concentrated in 
an equivalent condenser placed across the center of the line. There 
are, then, two parts of the circuit to consider. First : The portion 
extending from the generator to the center of the line, having a re¬ 
sistance and inductance equal to one-half of the total resistance and 
inductance of the line. Second : At the center of the line is a branch 
circuit consisting of two parts ; one having a resistance and inductance 
equal to one-half of the total line resistance and inductance, and the 
other a resistance and capacity equal to the total line capacity and 
line insulation. The joint impedance of these branches is to be ob¬ 
tained by either the method given on p. 351 or that on p. 353. 
Having obtained this joint impedance, it is necessary to add it to 
the impedance of the first portion of the circuit, remembering that the 
vector sum is the desired quantity. 

452. 2. A closer approximation may be obtained by dividing the 
line into any desired number of parts, attaching to each its proper 
resistance, inductance, and capacity, and obtaining the joint impe¬ 
dance of all these branches, as above indicated. In this way accuracy 
may be carried to any desired limit that the patience of the operator 
will permit. 

453. 3. As capacity is equivalent to a negative inductance, it 
can be shown 1 that for an aerial line uncomplicated by the resistance, 

1 See Traite de Telegraphie, par T. Tomas, p. 313. 


CONDUCTORS FOR ALTERNATING CURRENTS. 367 

inductance, and capacity of the receivers at the end of the line, the 
impedance may be expressed by — 

/ = V R 1 + (L — i CR 2 ) 2 o) 2 . (177) 

454. Tabular Values. — For all these methods, the capacity per 
unit of length of the line is required. Unfortunately, the capacity of 
a circuit is a function, not only of the geometrical relations of the 
conductors and the potential acting, but is also affected by the geo¬ 
metrical relations of the circuit to all other neighboring bodies. Thus, 
for the simple case of an ordinary aerial line, to accurately ascertain 
the capacity, consideration must be given not only to the two con¬ 
ductors, but to the presence of the poles, insulators, and cross-arms, 
or other supports, and also to the earth itself. If other conductors 
are in the immediate vicinity, the results are still further involved, 
while if the neighboring wires are under electrical action, the mutual 
reactions present a problem of the greatest complexity. If the 
mutual effect of two parallel wires of a radius r and separated by a 
distance d, is considered, while the reaction of neighboring bodies, 
the earth included, be neglected (which in a majority of cases is sen¬ 
sibly true), Mr. Heaviside 1 shows that the capacity is determined by 

the expression — 1 

C= ---. 

41og f - 
r 

Here the value of C is in electrostatic C. G. S. units. 

On Sheet 3, Table No. 44, f and f' are plotted for this value 
of C. To use these curves, the ratio of d/ r is found from the di¬ 
agonal scale a, Sheet 1, and the value of C is ascertained by fol¬ 
lowing a horizontal line from the value of d / r (found as previously 
described on Sheet 1), on the left-hand scale, to its intersection with 
the curve f or f', and then a vertical line to the top or bottom 
of the sheet. Here, on the scale marked — 

1 

i d’ 

4 logf - 
r 

will be found the value of C. To illustrate : Assume two bare wires, 
No. 00, are placed on insulators in a conduit 6" apart. As the 
conductor is 365 mils diameter, r = 183 mils (.463 cm.) and d = 6" 


1 Electrical Papers, vol. i., p. 43. 





368 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


(15 cm.). On Sheet 1, as already explained, find the value of d / r 
as 32.4, then turning to Sheet 3, find 32.4 on the left-hand scale 
marked “dj r” ; follow a horizontal line to the curve f, value of 

1 

, i d’ 

4 log* - 
r 

then follow a vertical to the top scale of the Table marked Values of 

1 

4 i d’ 

4 log* - 

r 

finding .074 as the desired capacity of the wires in electrostatic 
C. G. S. units, per centimeter of length. 

455. Usually capacity in microfarads per unit of length is a more 
convenient quantity for the purpose of calculation. The following, 
Table No. 45, gives the necessary multipliers sufficing to transform 
E. S. C. G. S. units into M.F. for each of the customary units of 
length. 

Table No. 45. 


Multipliers to Transform E. S. C. G. S. Units into M.F. per Unit of Length. 


E. S. C. G. S. Units 
Multiplied by 

Equals M. F. per 

E. S. C. G. S. Units 
Multiplied by 

Equals M.F. per 

.19 

Mile of 5‘280 feet. 

.000108 

Yard. 

.036 

1000 feet. 

to 

o 

Kilometer. 


456. Thus, in the example, .074 x T9 = .01405 M.F. per mile, 
it will be seen that the vertical scales d/ r, 2 h / r, and 2 h / d have 
two sets of numbers, one in heavy type, and one in light. There are 
two curves for each expression, one drawn with a heavy line, and one 
with a light line. Also, the horizontal scales for the heavy line 
curves will be found at the bottom of the sheet, and for the light 
line curves at the top. The heavy type on the vertical scales 
correspond to the heavy curves, the values of which must be read 
off on the scales at the bottom of the sheet, while the light-face 
type on the vertical scales corresponds to the light curves, values of 
which must be read on the scales on the top of the sheet. The heavy 
curves are drawn for the small values of dj r from 0 to 20, and the 
small values of 2 h / r and 2 h j d from 1 to 2,000 ; while the light 
curves are for larger values of d j r from 20 to 500, and the large 















CONDUCTORS FOR ALTERNATING CURRENTS. 


369 


values of 2 h j r and 2 Ji j d from 2,000 to 20,000. Having, by means 
of the Tables, ascertained the value of the line capacity per unit of 
length, the impedance may be determined by either of the above 
methods at the discretion of the operator. 

457. Sec. b. — One aerial wire with ground return. 

By means of the method of “ Images/’ as indicated on page 364, 
it can be shown that the capacity of an aerial wire with a ground 
return is given by the expression — 


4 l 0gf — 
r 

and the value of this formula may be at once derived as just de¬ 
scribed, by substituting 2 d for d. 

458. Sec. c. — Concentric Cables. 

When one of the conductors is rolled into a cylinder surrounding 
the other, forming a concentric cable, the geometrical relations of 
the circuit are not altered, and the capacity may be expressed by the 
same formulae, by substituting r\ the radius of the outer conductor, 
for d. In the formula — 

C = * _ 

n d ’ 

4 logf - 

r 

the value of C is for one unit of conductor length, and the total 
capacity is obtained by multiplying by the entire length of the 
circuit. In speaking of concentric cables, it is usual to consider the 
le 7 igth of the cable , which is only one-half the length of the circuit 
contained by the cable; and if the formula — 


C = 


1 

4 logf — 
r 


used to give the capacity of a cable, be multiplied by the length of 
the cable, the result will be only one-half the desired amount. It is 
necessary that the value of C be multiplied by the cable circuit or 
twice the length of the cable for the true capacity, and the formula 
reduces to the common expression — 








370 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


459 . Sec. d. — Effect of adjacent bodies. 

In the consideration of capacity effect, attention has only so far 
been given to the mutual reactions of the two conductors forming 
the circuit. If circuits were always perfectly insulated so as to be 
electrically separated from all other bodies, there would be no further 
modification ; but, in view of defective insulation, it becomes neces¬ 
sary to recognize the pressure of other bodies. Take the simple 
case of a single wire of radius r, set at a height Ji above the ground, 
with a ground return as modified by the pressure of an additional wire 
of the same size, set at a distance d from the first wire. Mr. Heavi¬ 
side shows (in the article above referred to) that, under these cir¬ 
cumstances, — 



(178) 


On Sheet 3, Table No. 44, there will be found, on the right-hand side 
of the center vertical scale, a set of diagonals a' for ascertaining 
the values of 2 h / d and 2// / r. The height above the ground h is 
on the top horizontal scale, while the diameter of the conductors and 
the distance between them will be found on the bottom scale ; the 
portion of the table is used in a manner similar to that given for the 
a on Sheet 1. As an example, assume a No. 00 wire 10 ft. from 
the ground, with a second No.00 wire 6" from it. Here, the dia¬ 
meter of the wire is 365 mils, hence r= 183, d — 6" = h = 10 ft. 
= 120". Find 2 h / d = 40, by following a diagonal from 6 on the 
lower bottom scale to its intersection with a vertical through 120 on 
the top scale, and then a horizontal to the scale marked “ 2// / d ,” 
finding 40 as the desired value. Find 2 h / r — 1,310, in a similar 
manner. Then determine the values of — 




and 


by following a horizontal from 1,310 to the intersection with the 
respective curves g' and h', and then a vertical to the lower scales, 
getting respectively 2.7 and 38.8 as the desired values. The value 



is gained in a similar manner, as 10.26, 















CONDUCTORS FOR ALTERNATING CURRENTS. 


371 


by following a horizontal through 40 to the intersection with the 
curve i, and then a vertical to the top scale, obtaining 10.26 ; 


then, 


C = 


2.7 


= .094 electrostatic C. G. S. units. 


38.8 — 10.26 

In a similar manner the effect of more than one adjacent wire 
may be obtained. The problem, however, soon becomes so complex 
as to be very difficult of solution. The addition of a second wire 
increases the capacity about 11 per cent, and with three more wires 
the increment is about 24 per cent. Probably the most important 
case of the effect of adjacent bodies is the consideration of the 
reaction of the earth on a complete metallic circuit. For this com¬ 
bination Mr. Heaviside shows that the capacity is given by the ex¬ 
pression — 


.4343 


C = 




log V 1 + 


d 


2 log 


— ( 2 log 


v/ 


1 + 


2 h 
d 


2 \ 2 


(179) 


The solution of this formula is made in the same manner as given 
for the preceding case. Assuming the same data as in the last 
example, — _ 1_39 


C = 


38.8 — 10.26 


= .048 electrostatic C.G.S. units. 


460. Character of Dielectric. — In the preceding formulae for 
capacity, the value of the specific inductive capacity of the dielectric 
has been assumed as 1, the value for air. Should any other sub- 
stance be used, the formulae must be multiplied by the proper co¬ 
efficient ky for difference in specific inductive capacity; the value for 
k will be found in Table No. 46. 


Table No. 46. 


Specific Inductive Capacity. 


Name of Substance. 

Specific Induc¬ 
tive Capacity. 

Name of Substance. 

Specific Induc¬ 
tive Capacity. 

Air. 

1 

Carbon Di-oxide 

1.00066 

Glass. 

1.90 to 3.013 

Hydrogen. 

.99967 

Shellac. 

1.95 to 2.740 

Vacuum. 

.99941 

Sulphur. 

1.93 

Yellow Wax. 

1.86 

Gutta-percha. 

2.580 to 4.20 

Resins. 

1.80 

Ebonite. 

2.284 

Hooper’s Composition . 

3.10 

India-rubber. 

2.220 to 3.70 

Mica. 

5.00 

Turpentine. 

2.1 GO 

Flint Glass, extra dense . 

6.55 to 10.10 

Petroleum. 

1.6 to 2.070 

Distilled Water .... 

76.00 

Paraffine. 

1.98 to 2.00 

Ozokerite. 

2.13 

Carbon Bi-sulphide . . 

1.810 

Pitile. 

1.80 













































THE ELECTRICAL TRANSMISSION OE ENERGY. 


f. I 


CHAPTER IX. 

SERIES DISTRIBUTION. 

Art. 461. Origin. — In the earliest attempts to distribute en¬ 
ergy by means of electricity, one source of supply, or generator, was 
connected directly with a single device for utilizing the energy pro¬ 
duced. The generator and receiver were separated by but a short 
distance; and thus a simple circuit of wire, sufficient to carry the 
small amount of current produced by the early dynamos, was amply 
sufficient for the purpose required. 

462. The next step in the development of distribution was the 
introduction of two or more receiving mechanisms placed succes¬ 
sively upon the same circuit. From this as a starting-point systems 
for supplying electrical energy have gradually grown until they have 
attained their present complexity, involving miles of mains receiving 
from central stations of immense size amounts of energy to be meas¬ 
ured by thousands of horse-power, and distributing the same over 
many square miles of territory. So long as a single generator sup¬ 
plied but one receiver, the load was a constant one, the receiver,, 
when running, absorbing all the energy delivered by the generator, 
and the generator operating under no load when the receiver was cut 
out of service. In modern systems the load not only varies in quan¬ 
tity from time to time, thus varying the demands placed both on the 
distributing system and upon the generators ; but often the load is a 
movable one, its position with reference to the generating-station 
constantly varying. Thus it is apparent that with the developments 
of new and additional methods for utilizing electrical energy many 
complicating factors have been introduced into the problem of distri¬ 
bution. 

463. Classification. — The quantity of energy carried by any 
circuit is measured by the product of two factors, one, the electro¬ 
motive force or pressure, being that unknown quality of this form of 
energy by means of which it is enabled to overcome resistance, and 
the other the quantity or amount of electricity, which, by the aid of 


SERIES DISTRIBUTION. 


373 


the electro-motive force, is set in motion, and is therefore capable of 
doing work. Three methods may therefore be employed for varying 
the amount of energy delivered by any circuit. If the quantity of 
electricity remains constant, the quantity of energy will vary directly 
as the electro-motive force. If the voltage is kept constant, and the 
quantity of current varied, the amount of energy transmitted will be 
in direct proportion to this variation. To state the relation in mathe¬ 
matical language, if Q be the quantity of energy, V the voltage of 
the circuit, and / the amount of current in amperes, Q varies directly 
as the product of VI. Thus it is apparent that by varying either of 
the factors, the amount of energy transmitted to any point may be 
consequently changed in any desired degree. It is also plain that a 
similar change could be effected by varying both the current and 
electro-motive force. For most purposes, however, the variation of 
both factors introduces undesirable complications to such an extent 
that this latter method is rarely, if ever, adopted. To recapitulate, 
therefore, circuits may be treated : — 

First. As constant current circuits. 

Second. As constant potential circuits. 

The problem of distribution under either of the preceding divis¬ 
ions may still further be varied by the relative position of the gen¬ 
erator and receivers. Under the supposition either of a constant 
current or a constant potential circuit, the receivers may either be 
placed at a constant distance from the generating-station, or may, 
from time to time, occupy a varying position with reference to the 
same. So four conditions arise under which distribution may be 
considered. 

1. Constant Current Circuits having the generators and 
receivers at fixed distances respecting each other. 

2. Constant Current Circuits having the generators and 
receivers at varying distances respecting each other. 

3. Constant Potential Circuits having the generators and 
receivers at constant distance respecting each other. 

4. Constant Potential Circuits having the generators and 
receivers at varying distances respecting each other. 

464. 1. Constant Current Circuits with Generators and Receivers 
at Fixed Distances. — From the first attempts involving a single 
generator delivering all of its energy to one receiver, the next 



374 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


step was to embrace along one circuit two or more receivers, placed 
one after the other. As the receivers were arranged succeeding 
each other, having the same current pass through all of them, this 
kind of circuit came to be known under the name of “ Series Dis¬ 
tribution.” The current through the entire circuit being a constant 
one, this method is particularly adapted to installations covering a 
large territory, in which the load throughout the entire area is essen¬ 
tially uniform. Municipal illumination, whether by arc or incan¬ 
descent lamps, is properly arranged by the series system. The 
operation of motors upon series circuits is perfectly feasible, espe¬ 
cially if the motor load be so reasonably constant that the machines 
may run steadily and uniformly. As all of the receivers are traversed 
by the same current, the conductor that successively unites them is 
most simply arranged along the sides of an irregular polygon of 
which the various receivers form the apices. The location of the 
line should therefore be designed by a careful examination of the 
proposed site of the circuit, in order to select among all of the possi¬ 
ble locations that which will give a polygon having the shortest total 
perimeter. Frequently the arrangement of city streets, or regula¬ 
tions of city authorities, militate against the selection of the shortest 
and most direct route for the circuit. The dictates of economy, 
however, indicate that special attention should be given to arranging 
the circuit with a view to attaining the minimum length of conductor 
that can possibly be selected. 

465. Location of Station. — After the location of the circuit is 
determined, it is entirely immaterial at which point upon the route 
the central station is placed. Should it be impracticable to locate 
the plant exactly upon the line of the route, it should be situated as 
near to it as circumstances will permit; and all locations giving the 
same distance measured along the line of the conductor from pole to 
pole of the generators are equally favorable. This latitude in the 
location of the central station is one of the most valuable properties 
of the series system ; for it allows the selection of the site of the cen¬ 
tral station to be entirely controlled by such conditions as economy 
in cost of real estate, availability of fuel, water supply, etc. 

466. Current Density in Main Circuit. — As soon as the loca¬ 
tion of the circuit is selected, it becomes possible to design the line. 
Here the engineer must make such a selection between the dimen- 



SERIES D/S TRIE UTION. 


375 


sions for the conductor as indicated by strict rules of economy, and 
those proscribed by the commercial limitations of manufactured goods, 
as will lead to the best and most economical design. The nature of 
the service to which the plant is to be applied is usually the chief 
governing condition ; so a reasonably accurate knowledge of the num¬ 
ber of receivers, the current and electro-motive force of each, and the 
resistance of the line, must be known, together with a parallel knowl¬ 
edge of the properties of the generators obtainable, in order that the 
supply and demand of station and line may be mutually adjusted. 
As the plant is to be a constant current one, in which all parts of 
the circuits are traversed by the same current, it is apparent that all 
the receivers must be capable of operating under this imposed cur¬ 
rent, and that only such receivers as can do so must be placed in the 
circuit. Only such generators as can supply this predetermined 
current can be used in the station. By varying the electro-motive 
force at the terminals of the receivers, different amounts of power 
can be supplied to different customers. 

Let / = the current selected for the line in amperes. 

E = the electro-motive force of the station. 
e, /, e", etc. = electro-motive forces of the different receivers, 
etc. = the number of each kind of receiver. 

R — the resistance of the line. 

L = the length of the line from pole to pole of the station. 

S = the cross-section of the conductor. 

p = the specific resistance of the conductor. 

The energy demanded by the receivers is evidently — 

2/( ne -f- n'e' -f- n"e" + etc.). (130) 

The resistance of the line is — 



In order to deliver a current of / amperes to the customers, an 
amount of energy equal to pLI 2 / 5 must be expended in the line ; 
the station, therefore, must supply energy to the amount of — 

EI = 5/ {ne + «Y+ «V'+ etc.) + EEL . (181) 

The number of receivers, the current, and electro-motive force required 
by them, with the length of the conducting circuit, are fixed by the 
general condition of service that the proposed plant is intended to 




376 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


perform ; so in equation (181) there remains E, p, and S as possible 
variables whose value is to be determined by the designer according 
to the best economic condition. Experience has eliminated all mate¬ 
rials except copper from circuits designed to supply power ; p, there¬ 
fore, may always be assumed as the specific resistance of this metal. 
In the selection of E, the engineer is limited to the existing commer¬ 
cial forms, of dynamos, or some combination of them. It is advisable 
to keep E as low as possible ; for with high potentials the danger 
and difficulties to be encountered, the probabilities of interruption to 
service, and the expense of maintenance are largely increased, thus, 
in reality, 5 becomes the important variable ; solving, then, for S, — 

£ __ pLI _ (T82) 

E — 2 {lie + n'ef n"E -f- etc.). 

For an exact solution of this equation the value of E must be known. 
This, however, as has been seen, may vary within what may be 
called commercial limits. Now, as the cost of the line varies quite 
closely with S, it becomes important to inquire into the conditions 
governing N and E that shall, in the most commercial manner, reduce 
original outlay and maintenance. 

The quantity I / Sis the current density per unit of area of the 
conductor, and is frequently used, lines being simply proportioned so 
that the current density shall not exceed a certain predetermined 
amount. 

467. Economical Conditions. — So long as electrical distribu¬ 
tions were comparatively of small magnitude, involving but a single 
generator supplying one receiver and requiring but a limited circuit, 
the question of economy in the conductors occupied but a small and 
subordinate field of consideration. A wire amply large enough to 
transmit all of the energy was introduced with but little thought as 
to the cost of the circuit. As soon, however, as systems of distribu¬ 
tion commenced to ramify over areas of magnitude, the cost of the 
copper conductors immediately arose to a position of great impor¬ 
tance, in many cases equalling, if not exceeding, the cost of the 
remainder of the plant; therefore rendering it imperative that their 
design should be treated with the utmost care along the lines of the 
most rigid economy. 

In designing a system of conductors, eight points must be care¬ 
fully considered in order to secure the best results. 




SERIES DISTRIBUTION. 


377 


1. The conductors must be so proportioned that the energy trans¬ 
mitted through them will not cause an undue rise of temperature. 

2. 4 he conductors must have such mechanical properties as to 
enable them to be successfully erected, and so durable as to require 
a minimum of annual maintenance. 

3. The conductors viay be so designed as to entail a minimum 
first cost in line construction. 

4. The conductors viay be designed to attain a minimum first 
cost for station construction. 

5. The conductors viay be so designed to reduce first cost of 
plant, and cost of operation and maintenance to a minimum. 

6. The conductors may be designed to secure minimum total 
first cost of installation. 

7. The conductors may be so designed as to secure maximum 
conditions of good service. 

8. The conductors may be so designed as to attain a maximum 
of income with a minimum of station first cost. 

468. Careful consideration of the foregoing conditions indicate 
such a degree of incompatibility between them that it is impossible 
to fully realize all in any one plant. The skill of the designer is, 
therefore, to be exhibited in such a selection of governing conditions 
as will, in each particular case, develop a maximum service with a 
maximum economy. Compliance with the first two conditions is 
necessary in all distributing installations ; for if either the safe heating 
limit, or working strength of the conductors be exceeded, the lines 
become positive sources of danger to life and property. 

469. 1. Design for Heating Limit. — In every conductor a cer¬ 
tain amount of energy is transformed into heat and wasted by being 
radiated from the conductor itself. 

The most economical size of conductor to be used for a particular 
installation will then depend largely upon the cost of producing 
energy ; for, if the station operating expenses are low, so that the 
cost of production is small, and cost of the conductors comparatively 
high, it is obvious that the least metal section consistent with safety 
should be selected, in order that the interest on the cost and the 
maintenance expenses of the conductor may be a minimum, and 
balance the cost of the amount of energy lost by transformation 
into heat. 



378 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


470 . On the contrary, where station operating expenses are high, 
and cost of conductor installation is comparatively low, the converse 
will hold true it being under these circumstances advisable to put a 
larger investment of capital into the conductors in order to reduce 
the losses in the line to a minimum. 

471 . It is conceivable that, under the first conditions, the cost of 
producing the energy lost in the conductors may be so great, that to 
attain the most economical arrangement the conductors should be 
so small that the energy transformed into heat would be sufficient to 
raise the conductors to a dangerous temperature. 

Notwithstanding the masterly investigations of Mr. Kennedy into 
the subject of the heating of conductors, to which reference has been 
ma.de in Chapter VII., there is yet hardly as much experimental knowl¬ 
edge on the subject as could be desired, so that electrical circuits are 
often located in situations to which Mr. Kennedy’s rules do not fully 
apply, or in which the service is of unexpected severity. 

The case of concentric conductors is one of peculiar interest. 
Here one conductor, being entirely within and inclosed by a second, 
can have little or no chance for radiating the heat developed in it 
unless the limit be kept to so low a point that the heat in the interior 
conductor may pass through the insulating envelope, through the 
second conductor, and thence through the exterior envelope, into the 
air, without developing in the central conductor a destructive tem¬ 
perature. Under such circumstances, a very large factor of safety 
must be allowed in the heating limit assigned. This point is par¬ 
ticularly emphasized in Mr. Kennedy’s deductions. Circuits of this 
kind are particularly liable to injury from overheating, as they are 
used to transmit very large quantities of electrical energy, and the 
pressure brought to bear on the designer to effect a saving of copper 
is usually severe. Such circuits are also usually inclosed in some 
form of conduit structure where the chances for radiation are ex¬ 
ceedingly poor. It is true that the conduits being buried in the earth 
are constantly surrounded by a low mean temperature, which greatly 
adds to the safety of the inclosed circuits ; yet, on the other hand, 
the lack of air circulation and poor conductivity, of either the earth 
or conduit structure, must not be lost sight of in planning for the 
dissipation of the heat inevitably evolved. For interior wiring, 
special pains should be exercised in the design of the conductors to 


SERIES DISTRIBUTION. 


379 


keep their maximum temperature well under control. While the 
rules of the various boards of Fire Underwriters (See Appendix to 
Chapter III.), if followed, are designed to afford ample protection to 
buildings carrying electrical circuits, there always exists a temptation 
on the part of the designer, as well as of the contractor and builder, 
to effect economy by using a minimum amount of copper, protected 
by a low grade of insulation ; by employing the cheapest and least 
efficient forms of interior conduits ; and to reduce the number of 
safety appliances to a minimum. The consumer, on the other hand, 
usually plans for less electrical service than his future requirements 
are certain to demand. Thus there is the constant tendency on the 
one side toward insufficient conductors and dangerous installations, 
and on the other toward the use of a current exceeding that even for 
which the circuits, conduits, and other appliances were designed. It 
is therefore essential to use particular care and to check the designs 
for size of conductors with the most unfavorable circumstances that 
can be applied to the location in which they are placed, as indicating 
the probable temperature that may be attained by the circuits. 

472. 2. Mechanical Strength. — It frequently occurs that the 
safe heating limit indicates a wire of so small a size as, mechan¬ 
ically, to be impracticable. All circuits, whether overhead, under¬ 
ground, or in interior conduits, require a certain amount of mechanical 
strength in order that the conductors may be introduced in their 
appropriate places with a minimum amount of installation expense, 
and without endangering the integrity of the line. The lines must 
likewise have sufficient strength to withstand for a reasonable period 
of time the natural wear and tear to which plants of this kind are 
subjected. It would at first sight appear that the conductors, after 
being installed either in underground conduits, or as house-wiring, 
should be exempt from disturbing influences, and would constantly 
retain their integrity. On the contrary, numerous causes are oper¬ 
ative, constantly exposing the circuits to disturbing influences, such 
as settlement and shrinkage of the structures in which the circuits 
are inclosed, the mischief done by rats and mice, necessary changes 
and rearrangement of the lines, and many other causes of similar 
description — all tending to affect the mechanical integrity of the 
conductors. 

In aerial circuits unusual snow or sleet loads, high winds, the 



380 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


abrasion of tree branches, etc., are constantly tending to destroy the 
conductors. Thus, in many cases, the safe heating limit may indi¬ 
cate a conductor too weak from a mechanical standpoint to be 
successful; and the introduction of such a circuit, while perhaps 
more economical in first cost, will, in a very short time, prove to be 
enormously expensive from the standpoint of maintenance. 

473. 3. Minimum First Cost of Line. — The first cost of 
any circuit is separable into three distinct elements : 

First. The actual cost of the copper necessary to transmit the 
required amount of energy. 

Second. The cost of insulating or protecting the same elec¬ 
trically. 

Third. The cost of installing or erecting the circuits. 

For installations simply for temporary purposes, such as the 
illumination of, or operation of motors for, the construction of 
public works, etc., in which the area covered is of small extent, and 
the plant only expected to run for a limited portion of time, the 
most rigid economy should be exercised in the design of the circuit, 
and in the provisions made for its introduction ; for it is obvious 
that the circuit being in use but for a short period of time, and in 
a location where the wire is likely to undergo considerable injury, 
will be subject to but very little salvage when the work for which 
it is installed is completed. Thus, under these circumstances, the 
cheapest kind of pole-line, with meager insulation, sufficient only 
for purposes of safety to the workmen, and embracing the smallest 
possible amount of copper, is the one to be selected. 

From such circuits it is rare to obtain more than one-third or 
one-fourth of the value of the line as salvage. 

The generating-plant, on the contrary, so far as dynamos and 
engine consist, is but little injured by service of this kind, and may, 
at the end of the work, be credited back at almost its full value. 
In such lines it usually pays to waste a large amount of energy in the 
conductors in order to reduce the first cost of the line to a minimum. 

474. With permanent distribution plants of large magnitude, 
such as are usually tributary to central stations, the first cost of the 
circuit, while it should receive careful consideration, should never be 
allowed to militate against the introduction of the very best possible 



SERIES DISTRIBUTION. 


381 


style of conductors adequately designed for the work thrown upon 
them, and protected by all the best known means, either in under¬ 
ground conduits or on the strongest and most substantially con¬ 
structed pole-lines. 

475. 4. Minimum First Cost of Station. — The minimum 
first cost of station is obviously incompatible with the minimum first 
cost of conductors, for, if the amount of metal in the conducting 
circuit be reduced to the lowest point of safety, a very much larger 
amount of energy will be lost in the circuit, and still an addi¬ 
tional amount usually escapes through leakage due to defective insu¬ 
lation. 

To obtain minimum first cost on station plant, it is essential to 
expend a much larger capital in the line, in order that the station 
plant may be enabled to deliver the requisite amount of energy to 
the various receivers, without being loaded with line losses. 

476. In city locations, where underground conduits are a 
necessity, the cost of the circuits is the largest item in the installa¬ 
tion of the plant. In order to avoid constant reopening of the 
streets to accommodate enlargements or extensions, it is advisable 
to work out the design of the conductors on a sufficiently large scale 
to meet all of the business that is likely to accrue for several years. 
The conductors under these circumstances will be much larger, and 
will cover a very much greater territory, than the immediate demands 
of the business will indicate, and will necessitate a corresponding 
investment. Yet a structure of this kind, carefully arranged to 
reduce the annual maintenance to a minimum is, under such circum¬ 
stances, a paying investment. The station, on the other hand, may 
be planned for a minimum of first cost, and the buildings so arranged 
that additional generating units may be added from time to time as 
the business grows. The utility, under such circumstances, of a 
super-abundance of copper in the conductors is also apparent, as it 
evidently affords to the station the ability to carry the load thrown 
upon it with the least expenditure of energy lost in the conductors 
themselves, and with the least initial investment of capital. 

477. 5. Minimum First Cost of Plant and Minimum Cost of 
Maintenance and Operation. — To reduce the initial cost of the 
conducting system to a minimum, it is necessary to employ the 
smallest mains consistent with safety. This plan causes consid- 


382 THE ELECTRICAL TRANSMISSION OF ENERGY. 


erable waste of energy in the leads by transformation into heat, 
thus increasing the cost of the operating expense by the amount 
required to produce this lost energy, and also necessitating such an 
additional expense in the construction of the station as is required 
to provide the additional amount of plant necessary to produce the 
energy wasted in the conductors, over and above that which is 
essential to supply the demands of the customers. Thus undue 
economy introduced by reducing the size of the conducting system 
may increase both the total cost of the plant and the cost of opera¬ 
tion. On the contrary, by using large mains of low resistance, the 
lost energy and cost of additional station capacity may be reduced 
to any desired amount, but only by a corresponding increase in the 
expense of the conducting system. 

478. There evidently exists in every plant a certain relation be¬ 
tween the cost of station equipment, conducting system, and lost 
energy that will reduce the sum of these three quantities to a mini¬ 
mum, indicating the conductor that in the long run will be the 
cheapest, both as regards the gross expense of installation and the 
cost of operation. The determination of this, the most economical 
cross-section of the conductor, is somewhat complicated, and must be 
made for each plant under its peculiar conditions of operation, with 
special reference to the following considerations : — 


First. 

Second. 

Third. 

Fourth. 

Fifth. 

Sixth. 

Seveiith. 

Eighth. 

Ninth. 

Tenth. 


Cost of station per watt of output. 

Cost of producing energy per watt. 

Cost of conductor per unit of cross-section and length. 

Cost of conductor insulation per unit of cross-section 
and length. 

Cost of erecting or installing the line (such as pole-line 
or conduit expense). 

Rate of interest on total invested capital. 

Rate of depreciation upon capital invested in the station. 

Rate of depreciation upon the cost of the metallic por¬ 
tion of the conducting system. 

Rate of depreciation upon the cost of the insulating por¬ 
tion of the conducting system. 

Rate of depreciation upon the cost of the conduit, or 
pole-line. 



SERIES DISTRIBUTION. 


383 


479. This problem was first proposed to electrical engineers by 
Sir William Thomson in 1881. The solution then suggested predi¬ 
cated that the total cost of the conducting system varied directly as 
the weight of the material employed for the conductors, and that 
it was simply essential to make the annual interest and depreciation 
upon the cost of the conducting system equal to the cost of the 
energy wasted therein. Closer investigation, however, indicates the 
advisability of considering as variables all of the afore-mentioned 
quantities. 

480. Scrutinizing the cost of conductors, their expense may evi¬ 
dently be divided into two parts — one the cost of the metal em¬ 
ployed, and the other the cost of the insulating material. The 
expense of bare wire and copper strips evidently varies as their 
weight or cross-section ; and the expense of the material for uninsu¬ 
lated lines may be expressed by the equation — 

y = bS, (183) 

in which y is the cost per unit of length, S' being the cross-section 
of the conductor expressed in any desired units, and b a constant 
depending upon the varying price of line material per unit of weight. 

Stranded cable is slightly more expensive than solid conductors, 
but this simply increases the value of b. 

481. While the amount of insulating material necessary to pro¬ 
tect wires and cables does not vary exactly with the area, the rate of 
variation for all of the more common forms commercially employed 
is so nearly proportional to the cross-section, that this rate may be 
assumed without serious error. So, for any given class or kind of 
insulation, the expense of the conducting system may, with sensible 
accuracy, be expressed by the equation, — 

y = a + bS, (134) 

in which a and b are constants, depending upon the mode of manu¬ 
facture, and the kind and quality of the insulation, and the current 
market price of the material used. To determine the constants of 
this equation for any particular make of conductor, or class and 
quality of insulation, the prices for three or four cross-sectional areas 
should be obtained, and their values plotted on a sheet of cross-sec¬ 
tion paper by assuming the axis X to be the axis of the areas, and 
that of Y the axis of cost. By obtaining three or four points in this 


384 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


way, and drawing through them a line, a curve of prices is obtained, 
the tangent to which, at any point, is expressed by the equation, 
y = a + bS, from which the cost of any desired size of conductors 
may be readily obtained. Some examples of such curves will be 
found in Chap. XII. 

482. By means of a similar train of reasoning and graphical con¬ 
struction, the cost of pole-lines, conduits, subways, or other structures 
necessary for the installation of the conducting system, may be ex¬ 
pressed and obtained by a similar equation — 

/ = a' + b'S, (185) 

in which y 1 is the cost per unit of length of the structure, and a' and 
b' are constants, depending upon the kind of line to be built, while X 
is the area of the conductor as before. 

483. The cost of the line installation, however, cannot be nearly 
so exactly determined for variations in the size of the conductors, as 
it is evident that the style of installation which is adopted is a very 
large factor in the rate of varation of the cost. In the ordinary pole¬ 
line, the cost will be almost precisely the same for a very large varia¬ 
tion in the cross-section of the conducting system ; for a single line 
of poles may be made to carry either one very small conductor, or a 
great many of large cross-section, the only additional expense en¬ 
tailed upon the additional number of wires being that necessary for 
the insulators, and the labor of putting the lines into place. Thus, 
for pole-line construction, the constant a' is a large proportion of the 
value of y, b'S being relatively small. 

484. In a similar manner, that fraction of the cost of under¬ 
ground conduits, which is embraced in the items of paving, excava¬ 
tion, construction of manholes, etc., is very nearly constant over very 
wide ranges of conduit capacity and line area, the cost of the ma¬ 
terial used for the ducts, and labor of placing the same, being the 
chief items that vary to any great extent with the size of the con¬ 
ductor. For a concrete conduit, for example, with bare wire mains, 
the value of b 1 is zero ; for this description of conduit can contain 
any desired cross-section of conductor, with no variation in the ex¬ 
pense of construction. The cost of placing the conductors in position 
should be included in the term b', and will also be found to be sensi¬ 
bly constant for all cross-sections, excepting for conductors of very 


SERIES d/s trib ution. 


385 


large size, but will vary considerably if the required conductor section 
is split into several parts. 

485. Equations for minimum first cost of plant, and minimum 
cost of operation and maintenance. 

Let i = the rate of interest charged against the plant in per cent. 

di = the rate of depreciation charged against the line in per cent. 
d c = the rate of depreciation charged against the conduit in per cent. 
L = the length of the conducting system in any desired units. 

U" = the annual charge against the line for interest and depreciation. 

The cost of the line will be — 

Ly = L [0 + bS) + (of + b'S)] ; ( 186 ) 

then, U" = L [(a + bS) X (t + di) + (a' + b'S) (i + d c )]. ( 187 ) 

For simplification, let 

a = L (a (i -f- di) + d (t + d c )), 

and (3 = L (b (i -f- di) -\- b' (t d c )); 

then, U" = a + (3S. (1^^) 

Let F = the number of hours per annum that the plant operates. 

K = the cost of producing energy per watt-hour, K.W.-hour, or H.P.- 
hour, 

then assuming the notation on page 375, P ! 2 L / 5 gives the energy 
lost in the line, and as 2/ (ne + etc.) is the energy supplied to the 
customers, the station must supply — 

r2 t 

2 I (yie + etc.) + ———— watts. 

The cost per annum of the energy lost in the line will be FpPLK / 6*. 
If K 1 be the cost per watt of output for equipping the station, and i 
and d s the rates of interest and depreciation on the station, then 

pPLK' r , 

^— 0 + O 

will be the annual charge for interest and depreciation on this ex¬ 
pense. If U' be the total cost per annum of the lost energy, then 

U' = BE- \FK +K’ (i + d,)\ ( 189 ) 

For simplification, let 

A = P LP [FK + K' (/ + ^)]; 



then, 





886 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


Let U= U' + U", then 


u — d + /3S + — i 


( 190 ) 


differentiating with respect to S, 



( 191 ) 


486. A consideration of this equation will reveal several impor¬ 
tant deductions. 

First. It will be noticed that the value of 5 obtained makes that 
fraction of U' which varies with 5 equal to U", indicating that the 
most economical area of the conductor to be employed is that in 
which the annual cost of energy expended in it is equal to the sum 
of the interest and depreciation on that fraction of the total capital 
outlay which is proportional to the weight of the conductor employed. 

487. It is also to be seen that inasmuch as E and L do not enter 
into this equation, the most economical section of the conductor 
depends simply upon the amount of current in the circuit, and is 
entirely independent, either of the voltage at the generators, or at 
the distance to which the energy is transmitted. 

488. In selecting the values for the various constants in the 
preceding discussion, considerable judgment should be exercised. 

The value of i, the rate of interest upon the total capital invested, 
will vary according to the location, and will naturally be made to 
conform to the prevailing rates of interest for money at the location 
of the plant. 

489. The rate of depreciation on the station, d s , will naturally 
subdivide itself into four constituents, the rate on the buildings 
being the least of these, which for fire-proof construction may be 
taken as low as 2 to 3 per cent, while for buildings of wood or of 
less permanent character this constant will vary from 5 to 8 per 
cent. The depreciation on dynamos, provided standard types of 
machines are selected, and are not allowed to be dangerously over¬ 
loaded, is also exceedingly small, varying from 2 to 4 per cent. 

490. For the prime movers, whether steam or water motors are 





SERIES DISTRIBUTION. 


387 


selected, the rate should be considerably higher, varying from 5 to 
10 per cent, while on the boilers, in the case of the steam plant, the 
rates of depreciation are greatest, and should be assumed at from 
8 to 16 per cent. 

491. For the constant d c , the depreciation upon the conduit or 
pole-line part of the conducting system also varies between widely 
different limits. 

492. Permanent structures, such as cement-lined or iron-pipe 
concrete conduits, or earthen-pipe conduits, undergo little or no depre¬ 
ciation, and for these structures d c may be assumed not to exceed 
2 per cent per annum. 

493. For wooden conduits or pole-lines, on the contrary, the 
value of d c should be from 10 to 20 per cent, depending on the loca¬ 
tion. In a similar manner d n the depreciation on the value of the 
circuits, may extend over a wide range. For lead-covered cables 
with the highest kind of insulation, placed in underground circuits, 
this factor may be almost neglected. For rubber-covered wire in 
underground conduits, or in exposed pole-lines in thickly settled 
cities, this constant should have a value of 20 per cent, or more, as 
the insulation is very rapidly deteriorated by the effects of gas and 
water. For the best insulation on heavy aerial lines d ( should vary 
from 5 to 10 per cent; but for the poorer kinds, such as underwriters’ 
wire, it should be 20 to 30 per cent. In cases where there are many 
trees, d t may be as high as 40 to 60 per cent. 

494. It is thus evident that, in determining the factors entering 
into the interest charge upon the cost of the plant, much careful con¬ 
sideration must be given, as usually the tendency is to place these 
factors so low that, after a short time of operation, the maintenance 
charges are found to be very much larger than was first estimated, 
and consequently sad inroads are made into the net profits of the 
plant. 

495. The determination of the factor K' is one which will vary 
considerably with the character of the plant under consideration. 
Apparently this value would be most properly computed by determin¬ 
ing the cost per watt of output, then assigning K' such a fractional 
part of this sum as is represented by the ratio of the lost energy to 
the total output. In many instances this value is correct. However, 
in the case of a large station, with a very short line, this would proba- 


388 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


bly give K' too great a value; while, on the contrary, in the case of a 
small station with a very long line, it would give K' too small a value. 
It is, therefore, essential to canvass each particular instance for itself, 
and assign to K' such a proportionate assessment of the total station 
value as seems to fit the particular circumstances. 

496. In a similar manner, in assigning a value to K, considera¬ 
tion must be given to the mutual relations of the line and station. 
Apparently K would be given by dividing the total operating ex¬ 
penses by the total output in watts ; and while this value in many 
cases is partially correct, there are frequent situations in which it 
departs widely from the true amount. The values of both K ' and K, 
and in fact all quantities of this nature, are most accurately ascer¬ 
tained by plotting a curve as indicated in Fig. 218, in which the axis 
of X indicates the varying output of the station, and that of Y either 

(in the case of K') the cost of installation, 
or (in the case of K) the cost of producing 
energy, and selecting for the desired value 
of K or K', that obtained from the equa¬ 
tion of a tangent to the curve at that 
particular point, representing the circum¬ 
stances in question. By this process, as¬ 
suming W to represent the capacity of 
the station, dK' / dW or dK / dW is ob¬ 
tained, instead of K / W or K' / W ; for 
in all such calculations the rate of variation of the factors entering 
into the problem is the true value desired. 

497. Conductor Tables. —To facilitate calculations for the most 
economical conductor cross-section, Professor Forbes in England, 
and Professor Cartwright in this country, have calculated a series of 
tables, involving the cost of erecting or laying one ton of copper and 
the interest and depreciation charges allowed upon the plant, from 
which the most economical current density per unit, of actual cross- 
section of conductor, can readily be ascertained. Extracts from these 
Tables are given in Table No. 47, A and B (pp. 390 and 391). 

In section A, the left-hand vertical column contains the rate of 
interest and depreciation, while the top horizontal line gives figures 
for the cost of laying, or erecting, one ton of copper. This cost 
is supposed to cover the entire cost per ton of the wire or cable,. 



Fig. 218. 

Diagram to Ascertain the Value 
of K or K'. 





SERIES D/S TRIE UTION. 


389 


with its insulation, pole-line, conduit, or other supporting struc¬ 
ture. 

In section B, the left-hand vertical column indicates the cost of 
energy, in terms of one electrical horse-power, at the terminals of the 
generating station, while the top horizontal lines give the area of 
the conductor in square inches, or in circular mils. This Table is 
calculated for a current of 100 amperes. 

The use of the Table may be best indicated by an example. Sup¬ 
pose, for instance, that the cost of laying one ton of copper is $600, 
and that Id per cent is allowed for the sum of the interest and depre¬ 
ciation upon the conducting system. Following the horizontal line 
opposite 12 per cent in the left-hand vertical column of A, until this 
line intersects the column headed $600, the number .144 is obtained. 

Assume also that the cost of producing one electrical horse-power 
is $60 per year. Taking the horizontal line opposite $60 in the first 
left-hand vertical column of Table B, follow the horizontal line along 
until the nearest corresponding number to 144 is obtained (in this 
particular example the number is exactly 144, being found opposite 
60). Running up this column to the top of the table, T 2 <fo of a square 
inch, or 280,104 circular mils, is obtained for the requisite cross- 
section of the conducting system to carry 100 amperes. 

If the desired current in the conducting system is any other 
quantity than 100 amperes, the cross-section of the conductor is 
obtained by solving a direct proportion thus: — 

100 (amperes) : proposed current :: Joo amperes) : the desired area. 

498. 6. The Conductors may be so designed as to secure 
a total minimum first cost of installation, irrespective of operation 
and maintenance. 

There arises frequent occasion to use an electric plant on work 
of more or less temporary nature, in which the total cost of the ma¬ 
chinery and operation must be charged against the work in question, 
as the circumstances are such as to preclude the credit of any sal¬ 
vage. Usually, under such conditions, the cost of operation cuts too 
small a figure to be regarded. The cost of line and generating-plant 
must for this case be made a minimum. Assuming the previous 
notation, the station must have a capacity to supply — 

El watts = 2 I {iid + n'e' + n"e" -}- etc.) + ’ 



390 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Table No. 47. — Section A. 


Cost of Laying One Additional Ton of Copper. 




$300 

$325 

$350 

$375 

$400 

$425 

$450 

$475 

*3 

C 

5 

.030 

.033 

.035 

.038 

.040 


.043 

.045 

.048 

6 

.036 

.039 

.042 

.045 

.048 


.051 

.054 

.057 

C/3 

7 

.042 

.046 

.049 

.053 

.056 


.060 

.063 

.067 

03 

4-> 

CL) £ 

3 <u 

8 

.048 

.052 

.056 

.060 

.064 


.068 

.072 

.076 

Jr S 

9 

.054 

.059 

.063 

.068 

.072 


.077 

.081 

.086 

O a 

<D c 

10 

.060 

.065 

.070 

.075 

.080 


.085 

.090 

.095 

u 

g £ 

12 

.072 

.078 

.084 

.090 

.096 


.102 

.108 

.114 

£ '3 

14 

.084 

.091 

.098 

.105 

.112 


.119 

.126 

.133 

O .3 
^ *0 













„ a 

16 

.096 

.104 

.112 

.120 

.128 


.136 

.144 

.152 

to a> 

2 Q 

18 

.108 

.117 

.126 

.135 

.144 


.158 

.162 

.171 


20 

.120 

.130 

.140 

.150 

.160 


.170 

.180 

.190 


25 

.150 

.163 

.175 

.188 

.200 


.213 

.225 

.238 



$500 

$550 

$600 

$650 

$700 

$750 

$800 

$900 

c 

5 

.050 

.055 

.060 

.065 

.070 


.075 

.080 

.090 

6 

.060 

.066 

.072 

.078 

.084 


.090 

.096 

.108 

C/3 

7 

.070 

.077 

.084 

.091 

.098 


.105 

.112 

.126 

<D , 

5- 

<D c 

CD 

8 

.080 

.088 

.096 

.104 

.112 


.120 

.128 

.144 

J~ u 
o £ 

9 

.090 

.099 

.108 

.117 

.126 


.135 

.144 

.162 

v*_t a 
<D C 

10 

.100 

.110 

.120 

.130 

.140 


.150 

.160 

.180 

CJ 

£ g 

12 

.120 

.132 

.144 

.156 

.168 


.ISO 

.192 

.216 

& -3 

14 

.140 

.154 

.168 

.182 

.196 


.210 

.224 

.252 

O rt 













i < • r-< 













< a 

r-H D- 

16 

.160 

.176 

.192 

.208 

.224 


.240 

.256 

.288 

TO 03 

c G 

18 

.180 

.198 

.216 

.234 

.252 


.270 

.288 

.324 

c 

< 

20 

.200 

.220 

.240 

.260 

.280 


.300 

.320 

.360 


25 

.250 

.275 

.300 

.325 

.350 


.375 

.400 

.450 



$1000 

$1100 

$1200 

$1400 

$1600 

$1800 i 

$2000 


5 

.100 

.110 

.120 

.140 



.160 


.ISO 

.200 

c 

d 

6 

.120 

.132 

.144 

.168 



.192 


.216 

.240 

■*-> 

7 

.140 

.154 

.168 

.196 



.224 


.252 

.2 S 0 

*-i • 

CD £ 

■*-* L- 

8 

.160 

.176 

.192 

.224 



.256 


.288 

.320 

hh o 

S 

9 

.180 

.198 

.216 

.252 



.288 


.324 

.360 

»-t—i CD 

<4 c 

10 

.200 

.220 

.240 

.280 



.320 


.360 

.400 


12 

.240 

.264 

.288 

.336 



.384 


.432 

.480 

S -2 

O ^ 

14 

.280 

.308 

.336 

.392 



.448 


.504 

.560 

7? 

16 












U 

a 

.320 

.352 

.384 

.448 



.512 


.576 

.640 

£ <u 
c 0 

18 

.360 

.396 

.432 

.504 



.576 


.648 

.720 

c 

< 

20 

.400 

.440 

.480 

.560 



.640 


.720 

.800 


25 

.500 

.550 

.600 

.700 



.800 


.900 

1.000 





























































SERIES DIS TRIE UTION 


391 


Table No. 47. — Section B. 


Sectional Area for 100 Amperes in Square Inches and Circular Mils. 


& 

< . 

















o 

Cl 

-h 

CO 

CO 

o 

cl 


CO 

00 


Cl 

3 



Cl 

CO. 

lO 

o 

CO 

LO 

Tf 

Cl 

co 

o 

rH 

3 


8 


l- 

CO 

Ss 


1>T 

Cl 

vH 

o 

Cl 

LO 

r-l 

g 

CO 

o 

o 

CO 

CO 

cT 

Cl 

Cl 

iH 

Tt« 

o 

Cl 


O 

u 



y—^ 

T"i 

§ 

Cl 

c5 

Cl 

Cl 

Sq. Ins. 


.10 

.11 

.12 

.13 

.14 

.15 

.16 

.17 

.18 

.19 

.20 

.21 

.22 

S o 

4-» 

u c 

25 

291 

240 

202 

172 

148 

129 

114 

101 

090 

081 

073 

066 

060 

30 

349 

289 

242 

207 

178 

155 

136 

121 

108 

097 

087 

079 

072 

o 2 
g ta 

« .H 

<D CJ 

35 

407 

337 

283 

241 

208 

181 

159 

141 

126 

113 

102 

092 

084 

40 

465 

385 

323 

275 

238 

207 

182 

161 

144 

129 

116 

105 

096 

C 9 
<u *-« 
bJO D- 

45 

524 

433 

364 

310 

267 

233 

204 

181 

162 

145 

131 

118 

108 

<u 

" 'O u 
rt 0 

SJ rt 

50 

582 

481 

404 

344 

297 

259 

227 

201 

180 

161 

146 

132 

120 

55 

640 

529 

445 

379 

327 

285 

250 

221 

198 

177 

160 

145 

132 

J> cs £ 

J (i J) 

60 

698 

577 

485 

413 

356 

310 

273 

241 

216 

193 

175 

158 

144 

o ?. 

a. u " 

1 M M 

65 

757 

625 

526 

448 

386 

336 

295 

261 

234 

209 

190 

171 

156 

<u 

c/d v- 

70 

815 

673 

566 

482 

416 

362 

318 

281 

252 

225 

204 

185 

168 

o •*-» h 
^ c 

75 

873 

721 

606 

517 

445 

388 

341 

302 

270 

241 

219 

198 

180 

p ^ i—< 

rt u-i o; 

80 

931 

769 

647 

551 

475 

414 

364 

322 

287 

257 

233 

211 

192 

.a ° £ 

i: ° 

85 

989 

817 

687 

585 

505 

440 

386 

342 

305 

274 

248 

224 

204 

u « cu 

<U ^ 

90 

1047 

865 

727 

620 

534 

466 

409 

362 

323 

290 

262 

237 

216 

« g > 

95 

, , 

914 

768 

654 

564 

491 

432 

383 

341 

306 

277 

251 

22S 

Si 1 

100 

. 


808 

689 

594 

517 

455 

403 

359 

322 

291 

264 

240 

»-*—« -S 

105 




723 

624 

543 

477 

423 

377 

339 

306 

277 

252 

b/) 

110 





653 

569 

500 

443 

395 

355 

320 

290 

264 

c/5 

R g 

115 





, , 

595 

523 

463 

413 

371 

335 

304 

276 

*5 '3 

rt C 

3 

c 








546 

483 

431 

387 

349 

317 

288 









505 

449 

403 

364 

330 

301 

c 

< 









• • 

467 

419 

378 

343 

313 

& 

< . 

►J {/) 

D J 


co 

8 

CO 

£ 

8 

00 

Cl 

8 

CO 

t- 

co 

o 

T* 

CO 

Cl 

Cl 

s 

o 

Cl 

o 

co^ 

TP 

Cl 

CD 

LO 

r-* 

CO 

co 

00^ 

o 

Cl 

CD_ 

u 


Cl 

o 

Cl 

O 

o 

CO 

00 

y-* 

CO 

t-H 

CO 

CO 

CO 

CO 

CO 

LO 

CO 

cT 

co 

CO 

y-* 

CO 

CO 

Tf 

o 

CO 

o 

Cl 

01 

co 

i£ 

3 

Sq. Ins. 


.23 

.24 

.25 

.26 

.27 

.28 

.29 

.30 

.31 

.32 

.33 

.34 

.35 

i g 

25 

055 

051 

047 

043 

040 

037 

035 

032 






<—< 

30 

066 

061 

056 

052 

048 

045 

042 

039 

036 





1- 3 
o .2 

35 

077 

071 

065 

060 

056 

052 

048 

045 

012 

040 




2 « 

40 

088 

081 

074 

069 

064 

059 

055 

052 

018 

045 

043 

• • 

• • 

C 0) 

<D 1-1 

45 

099 

091 

084 

077 

072 

067 

062 

058 

054 

051 

048 

045 

• • 

« 2*~ 

50 

110 

101 

093 

086 

080 

074 

069 

065 

061 

057 

053 

050 

048 

a: q 

u 

55 

121 

111 

103 

095 

088 

0S2 

076 

071 

067 

063 

059 

055 

052 

0) C J-. 
k ^ <u 

60 

132 

121 

112 

103 

096 

089 

083 

076 

073 

068 

004 

060 

057 

2 « 5 

V* <« tJO 

i S ^ 

in ^ "C 

65 

143 

131 

121 

112 

104 

097 

090 

084 

079 

074 

069 

065 

062 

70 

154 

141 

131 

120 

112 

104 

097 

091 

085 

080 

075 

070 

067 

u « c 

° a rt 

75 

165 

152 

140 

129 

120 

111 

104 

097 

091 

085 

080 

076 

071 

,- . iT 

aJ ^ <u 
.2 ° £ 

80 

176 

162 

149 

138 

128 

119 

111 

103 

097 

091 

086 

081 

076 

85 

187 

172 

158 

146 

136 

126 

118 

110 

103 

097 

091 

086 

081 

o « H, 

90 

198 

182 

167 

155 

144 

134 

125 

116 

109 

102 

096 

091 

086 

1 '3 > 

95 

209 

192 

177 

164 

152 

141 

131 

123 

115 

108 

102 

096 

090 

Si § 

100 

220 

202 

1S6 

172 

160 

148 

138 

129 

121 

114 

107 

101 

095 

o ^ c 

105 

231 

212 

195 

181 

168 

156 

145 

136 

127 

119 

112 

106 

100 

o c/5 

. w) 

110 

242 

222 

204 

189 

176 

163 

152 

142 

133 

125 

118 

111 

105 

w J2 .S 
O rt "d 

115 

253 

232 

214 

198 

184 

171 

159 

149 

139 

131 

123 

116 

109 

.2 ^ 

2 H 2 

P 


264 

242 

223 

207 

192 

178 

166 

155 

145 

136 

128 

121 

114 


275 

253 

233 

215 

200 

186 

173 

162 

151 

142 

134 

126 

119 

a 

< 

• • 

286 

263 

242 

224 

208 

193 

180 

168 

157 

148 

139 

131 

124 








































































































392 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


if K' is the installation cost per watt of output, 
K' 2 / {tie + n'e' + ri'e" + etc.) + 


pZZ 2 

Z 


is the cost of the station. 

The cost of the line is (see equation (186)) 

Z \_(a + bS) + {o' + ^ r Z)] ; 

so that the total cost of the plant is — 

r 2 


U = K 


■rt 


2 I O + + «"/' + etc.) + All 

' W)J 


Z [(a bS ) + ( d’ + 

(192) 


for which a minimum must be obtained. 

Differentiating, dU = ) A-p rf [Z (/>Z + ZZ)] ; (193) 

<J 

— E-AA + L (b + £') dS = 0 ; 

— = - x 0 + <0; 

Z 2 


zz 


A^pZ 2 


z 2 


= z (£ + Z) ; 


A^p/ 2 _^ 2 . 

Z (* + Z) 

s = J^VL 1_ 
V z + A) ‘ 


(194) 


499. The value of Z thus obtained must be used with due regard 
to the precautions indicated on page 377. It is also necessary to con¬ 
sider carefully whether the length of time during which the plant 
will be in use, and whether the circumstances of operation, are such 
as to cause interest, depreciation and cost of lost energy to become an 
appreciable factor. 

500. 7. Design for the Accomplishment of Best Service. — 

The preceding paragraphs have treated at length the method for 
determining the minimum cost of a plant to accomplish a given 
service. In many instances, however, this factor is not the most 
important one in the solution of the problem, for the reason that 
the conditions of minimum expense will militate against the accom¬ 
plishment of a satisfactory service to the consumers. In series 
circuits, where the line is intended for a constant current, the calcu- 

















SERIES DISTRIBUTION. 


393 


lation of the conductor can usually be accomplished along the lines 
indicated under the previous headings. 

501. In other forms of distribution, however, as, for example, 
upon the parallel system, the conductors must be so arranged as to 
deliver to the consumer a certain definite pressure. Inasmuch as the 
variation in the potential at the different points along the mains is a 
function of the amount of current transmitted, and as the amount of 
current will depend upon the demands of the conducting system, it 
becomes essential to so design conductors, irrespective of economy, 
that the pressure required at the various points of the conducting 
system shall not vary too greatly. 

502. Under such conditions, service requirements, rather than 
the dictates of maximum economy, must govern the design of the 
conductors. This case, however, will be more extensively treated in 
the sections upon multiple arc distribution. Other circumstances, 
however, frequently arise in which service conditions should govern 
the size selected for the conducting system. The endeavor of the 
capitalist is always to reduce initial investment to a minimum, but 
there is no better guaranty of a paying investment than uniformly 
successful service. 

503. 8. Minimum Cost of Plant to Attain a Maximum In¬ 
come. — The income to be derived from a distributing-plant must 
not be lost sight of in the design of the conducting system ; and in 
some cases, though rarely, this becomes so important a factor as to 
govern the design. 

In locations where power is cheap, and transportation facilities 
are such as to largely increase the cost of materials, it would, from 
the standpoint of economy solely, be advisable to design the conduct¬ 
ing system according to Sec. 3. In many cases, however, this might 
lead to the expenditure of so large an amount of the station output 
in the conducting system that the load on the station might be so 
close to the total station capacity that the losses entailed in the con¬ 
ducting system would prevent service to the maximum number of 
consumers that could otherwise be placed upon the line. To increase 
the station capacity sufficiently to serve a very small additional pro¬ 
portion of consumers, might add so largely to the station cost as to 
be prohibitive, on account of the commercial size of the units of 
machinery obtainable. On the contrary, by increasing the size of the 


394 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


conductors, so as to reduce the losses in the line, the station may be 
able to supply sufficient additional power to accommodate the desired 
customers. Under these circumstances it may be exceedingly advis¬ 
able to increase the size of the mains, and correspondingly, their cost, 
to such an extent as to allow the station to supply additional custom¬ 
ers without incurring the expense of a large building and additional 
prime movers and their generators. 

504. Calculation of Loads. — In order to properly arrive at 
the most advantageous proportion for the relation of the line to the 
station, it is essential to accurately determine the conditions of load 
under which the plant will operate. 

For series circuits the solution of the problem is facilitated by 
the fact that the amount of current is a constant quantity during the 
entire time that the circuit is under operation. Therefore, to obtain 
the requisite data for calculating the load, it is simply essential to 
ascertain for each day in the year the number of hours that the 
circuit is likely to be in operation, and take the sum. 

As series circuits are chiefly employed in lighting installations, 
Tables Nos. 48, 49, and 50 are given as indicating the average 
number of daily hours of service for each month in the year. Cir¬ 
cuit loads can by this means be easily estimated. 

505. Regulation. — Systems to work under series distribution 
can only be regulated by varying the voltage or the pressure at the 
central station to correspond with the changes in load thrown upon 
the distributing system. From this cause, automatic regulation can 
only be perfectly mechanically attained in the simple example of the 
transmission of power between two similar dynamos, one serving as 
a generator while the other acts as a motor. 

506. For ordinary distributing-plants two methods are adopted 
to secure regulation under the varying load. If it is desired to throw 
out of service one or more of the receivers, it is necessary to short- 
circuit those whose service is to be discontinued, in order not to 
interrupt the rest of the line. If this is done, it is evident that the 
resistance of the entire line has been decreased by the amount due 
to the receivers that have thus been short-circuited. Thus, the 
equilibrium of the line has been disturbed, and the current increased 
just in proportion to the diminution of the resistance. It is practi¬ 
cable to maintain equilibrium by substituting for the short-circuited 


SEIZES DISTRIBUTION. 


895 


Table No. 48. 

Hours of Lighting.—Giving Approximate Daily Number of Hours from Sunset to 
Sunrise, and from Sunset to Midnight for each Month in the Year. Standard 
Time, Latitude 42° N. 


Name of Month. 

No. of Hours from 

Name of 

Month. 

No. of Hours from 

Sunset to 
Sunrise. 

Sunset to 
Midnight. 

Sunset to 
Sunrise. 

Sunset to 
Midnight. 


H. M. 

H. M. 



H. M. 

H. M. 

January . 

14.20 

7.0 

July . . 


9.11 

4.30 

February . 

13.20 

6.28 

August 


10.05 

5.10 

March. 

12.12 

5.50 

September 


11.33 

5.52 

April. 

10.40 

5.20 

October . 


12.48 

6.40 

May. 

9.37 

4.50 

November 


14.00 

7.17 

June. 

8.48 

4.28 

December 


14.24 

7.26 


Table No. 49. 

Showing Hours of Lighting Exclusive of Sundays and Four Holidays. 

Taken from actual records of the average time of lighting during three years, including fogs and dark days. 


Hours of Lighting. 

Period of the Year 
During which Light is required 
at these hours. 

Total Number 
of Hours 
cf lighting per 
annum. 

6 a.m. till daylight. 


October 1 to March 15. 

200 

Dusk till 5.30 p.m. 


October 1 to March 1. 

150 

Dusk till 6.30 p.m. 


September 7 to April 1. 

300 

Dusk till 7.15 p.m. 


August 15 to May 1. 

400 

Dusk till 7.45 p.m. 


August 7 to May 11. 

600 

Dusk till 8 p.m. 


July 28 to June 5. 

800 

Dusk till 9 p.m. 

> 


1,050 

Dusk till 10 p.m. 



1,440 

Dusk till 11 p.m. 



1,800 

Dusk till midnight. 


^ All the year. 

2,150 

Dusk till 2.15 a.m. 



3,000 

All night. 



4,300 


Table No. 50. 


Showing Hours of Lighting Throughout a Year of 8,760 Hours. 


Daily Lighting. 

January. 

February. 

March. 

April. 

May. 

June. 

July. 

h 

t/5 

D 

3 

< 

September. 

October. 

November. 

December. 

Total per 
Annum. 

From sundown to 8 p.m. 

125 

89 

67 

36 

6 


• • 

21 

54 

87 

117 

140 

742 

From sundown to 9 p.m. 

156 

117 

98 

66 

37 

20 

25 

52 

84 

118 

147 

171 

1091 

From sundown to 10 p.m. 

187 

145 

129 

96 

68 

50 

56 

83 

114 

149 

177 

202 

1456 

From sundown to 11 p.m. 

218 

173 

160 

126 

99 

80 

87 

114 

144 

180 

207 

233 

1821 

From sundown to midnight . . . 

249 

201 

191 

156 

130 

110 

118 

145 

174 

211 

237 

264 

2186 

From sundown to 2 a.m. 

311 

257 

253 

216 

192 

170 

180 

207 

234 

273 

297 

326 

2916 

From sundown to 4 a.m. 

373 

313 

315 

276 

254 

230 

242 

269 

294 

335 

357 

388 

3646 

From 4 a.m. to sunrise. 

125 

92 

69 

32 

3 

• . 

• • 

24 

51 

75 

103 

154 

728 

From 5 a.m. to sunrise. 

94 

64 

38 

2 





21 

44 

73 

123 

459 

From 6 a.m. to sunrise. 

63 

36 

r r 
( 







13 

43 

63 

254 










































































396 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


receiver an equivalent resistance. But by this device no economy is 
introduced, for the entire circuit is then expending precisely the 
same amount of energy as it was previously called upon to deliver. 
Even in cases where the power costs little or nothing, it is necessary 
to complicate the installation by separate pieces of apparatus to 
accomplish this short-circuiting that shall be capable of absorbing 
and destroying, by conversion into heat, the amount of energy 
usually taken by the receiver. 

507. In order to avoid loss of power, it is sometimes practicable 
to introduce devices for short-circuiting the receivers, which shall 
substitute for the receiver an apparatus which will introduce into 
the circuit an opposing electro-motive force equivalent to, or produ¬ 
cing the same effect, as the receiver itself. This method is widely 
applied to alternating current circuits under the various forms of 
choking or reactive coils. The arrangement consists of an electro¬ 
magnet, having a divided core, preferably with a closed magnetic 
circuit. The self-induction of the coil is so calculated as to produce 
at its terminals an electro-motive force of opposite sign equivalent to 
that of the apparatus which has been short-circuited. Under these 
circumstances, neither the current nor electro-motive force of the 
generators has been changed; but their difference of phase has 
been slightly altered, thereby effecting a saving of energy equal to 
that previously expended in the short-circuited receiver. Alternat¬ 
ing circuit devices of this kind practically save all of the energy 
that would be otherwise expended in the receivers, excepting the 
small amount absorbed by the reaction coil, which is usually in¬ 
appreciable. 

508. A second method of regulation, which is less simple and 
less economical in its effect upon the energy dispensed in the circuit, 
may be applied to constant current machines, in which the reactive 
coil is inoperative. This scheme of regulation consists in applying 
to the dynamo machine a regulating apparatus which shall affect the 
potential delivered at the terminals of the machine itself. All de¬ 
vices of this kind involve an electro-magnet, which is excited by the 
current delivered by the machine. When, by the short-circuiting of 
any of the receivers, the resistance of the line is decreased, there is 
a proportionate increase in the quantity or current sent out by the 
generator. This addition to the line current, flowing through the 


SERIES DISTRIBUTION. 


397 


regulator, excites the electro-magnet, forming a part of the apparatus, 
to a greater degree, thereby setting in motion a train of mechanism 
which may be arranged to accomplish either of the three following 
results : — 

509. 1. The regulator may be so arranged as to shunt or dimin¬ 
ish the current flowing through the field magnets of the generator. 
Under these circumstances, a decrease in the current flowing through 
the fields decreases the number of magnetic lines in the magnetic 
circuit of the generator ; and this weakening of the magnetism is fol¬ 
lowed by a proportionate decrease in the voltage of the machine, 
thereby restoring the balance of the circuit. 

510. 2. The regulator may be so arranged as either to increase 
the air-gap, or to short-circuit a part of the magnetic circuit of the 
generator, thereby accomplishing the same result in 'decreasing the 
voltage of the machine. 

511. 3. The regulating mechanism may be arranged so that on 
the increase of current flowing through the circuit, the regulator 
shall automatically shift the brushes on the dynamo away from their 
position of maximum voltage to some other place on the commutator, 
thus giving a decrease in the pressure developed by the machine. 

512. While many of these devices have mechanically been 
brought to great perfection and are eminently successful, yet this 
method of government is attended by difficulties involving a loss of 
economy or danger to the commutator, or other parts of the gener¬ 
ator, to such an extent that series circuits are rarely selected for 
distribution under any circumstances excepting those involving loads 
which are expected to be reasonably constant during the greater 
part of the time in which service is expected. 

513. Series distribution, therefore, possesses the advantage that 
the amount of current can never exceed a certain predetermined 
limit. This presents security against the chances of danger from 
short-circuiting, for a sensible loss of current is immediately in¬ 
dicated by the irregular action of the receivers that may lie between 
the points of leakage. This quality is not possessed by other methods 
of distribution. On the contrary, the series system has the disad¬ 
vantage of a lower efficiency for the percentage of energy expended 
in the circuits, and is only constant so long as the resistance and the 
current remain mutually unchanged. Therefore the efficiency falls 


398 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


in proportion to the number of receivers that are put out of com¬ 
mission. 

514. Automatic Cut-outs for Series Circuits. — A great num¬ 
ber of devices have^been arranged for the purpose of automatic cut¬ 
ting out of the various receivers on series circuits. These devices 
may be divided into two classes. 

Lamp Cut-outs. — These devices, operating on and especially 
adapted to arc lamps, are so arranged as to cut the lamp out of 
circuit as soon as the carbons are entirely consumed. All such 
contrivances are based upon a differential magnet, so planned that 
when the resistance of the circuit, due to the increase in the length 
of the arc, becomes sufficiently great, a portion of the circuit will be 
shunted into a fine wire coil on the differential magnet, and by closing 
its armature, will cut the lamp out of series. 

515. Time Cut-outs. — Other automatic cut-outs are arranged 
upon the principle of allowing the translating device to operate for 
a certain number of hours, and then cut it out of the circuit. These 
devices are usually based upon the application of a clock to a shunt 
operated by an electro-magnet, so arranged that after the receiver 
has operated a certain number of hours, the clock mechanically 
closes the shunt, throwing the current around the receiver. Such 
devices are applied to cut out constant current motors, and also to 
cut out arc lamps that are contracted to burn a certain, definite 
number of hours each day. 

While contrivances of this kind have evinced remarkable ingenu¬ 
ity on the part of their inventors, and while on some circuits they 
form valuable adjuncts, they add so great a degree of complexity, 
and require so much additional maintenance expense, that their 
utility is, in many cases, quite questionable. 

516. Designs for Series Circuits. — In the use to which series 
circuits are most frequently applied, namely, for municipal illumina¬ 
tion, it is obvious that the greater part of the plant load will be 
thrown on at about sundown, and will remain essentially constant 
throughout the entire hours of the night, all of the lamps being 
simultaneously extinguished at the succeeding sunrise. Thus, under 
these circumstances, the plant load is essentially a constant quantity 
during its entire time of service ; and while during different periods 
of the year the varying lengths of night and day, or the demand 




SERIES DISTRIBUTION. 


399 


caused by cloudy and stormy weather, is of such a nature that, while 
it increases or decreases the length of time that the plant is at work, 
it does not vary to any appreciable extent the load which the plant is 
called upon to carry. 

517. Arc-light installations are frequently designed to supply 
commercial lights in addition to those used for city lighting. The 
commercial lights in interior locations may be called upon to run at 
very different periods of time than those demanded for municipal illu¬ 
mination ; but the conditions giving rise to the demand for such 
lights will naturally be tolerably constant throughout the territory 
that would ordinarily be embraced by the lighting plant. So while 
the length of time that commercial lamps would be required to burn 
might be very different from that called for by the city lighting, yet 
both the commercial and municipal loads would be reasonably con¬ 
stant quantities. Many attempts 
have been made to so plan arc 
circuits that the commercial load 
will be separated or rendered dis¬ 
tinct from the municipal load. 

This can always be done by run¬ 
ning independent circuits for each 
kind of service; yet this plan 
naturally entails a certain amount of waste conductor material, for 
while the commercial lights may be required at an earlier hour than 
the municipal lights, and also may be extinguished at an earlier hour, 
yet for the great proportion of the time both kinds of service are 
simultaneous. 

Any design of circuits, therefore, which can be made so that at 
least for a part of each day one circuit may be used for both sets of 
lamps, will result in a corresponding saving in copper expense for 
the original circuit. 

518. One method for introducing a saving in the copper required 
for circuits containing both commercial and municipal arcs has been 
proposed by Mr. Sharpstein, in the Electrical Engineer. This method 
is shown in Fig. 219. 

Two machines were installed in the station indicated at No. 1 
and No. 2, and the circuits so arranged that all the commercial 
lamps were on wire G, while all the municipal lamps were on wire F. 




-¥r- 

-x- 

—*— 



— * - 






















t 


E 

C 


NO. 2 


F 

B 


G 

A 


NO. 1 


Fig. 219. Diagram of Series Lighting. 











400 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


When the commercial lamps were placed in operation, machine No. 1 
was started, and with the switchboard, cables, and plugs, A and G were 
connected, and B and E. When service was needed for the munici¬ 
pal lamps, machine No. 2 was started, the brushes being placed at 
the point of minimum working capacity. Then, by means of the 
remaining hole in the terminal B, machine No. 1 was connected with 
C, and by means of the remaining hole in E the third wire leg was 
connected'with D. As a result, machine No. 2 was in circuit with 
no load ; and if the brushes had not been placed at the point of mini¬ 
mum capacity, a burn-out would have occurred. Now, by connecting 
E and B, both machines are placed upon the commercial circuit, and 
in order to cut E out and get F into circuit, one plug of the cable, 
just removed from the switchboard, should be placed in the remain¬ 
ing hole at D. The other plug is put into the right hand, and held 
near F until the plug in E is withdrawn far enough to draw a short 


DOWN TOWN STATION 




1 45 LAMPS <- U 

P TOWN STATION 

) -c- 

/+ 



A P B 

2 CLEAR - LEG. \c 

3 CLEAR -LEG. J ) 

•*— 45 LAMPS '• 

A 

M : 


»± 





4 40 LAMPS -" 


Fig. 220. Arc-Lamp Circuit. 


arc, when the plug in the right hand is put into one of the holes in 
F, when the arc at E is extinguished, and both lamp-legs are on both 
machines. 

519. There are many obvious objections to running dynamos in 
series, as is required by the preceding method. The geographical 
location of the respective commercial and municipal arcs is not 
always such as to enable the saving of an appreciable amount of cop¬ 
per. Mr. C. G. Young has indicated two methods, as shown in the 
accompanying illustrations, which avoid the difficulties of placing 
the dynamos in series, and yet accomplish a notable saving of copper. 
In Fig. 220 three dynamos are shown as operating three circuits, 
which may be arranged either to run conjointly or independently, 
with four wires instead of six. A little study of the diagram will 
render the operation of the currents entirely clear. If all the lamps 
are in operation at once, it is evident that wires Nos. 2 and 3 will 
carry double the current of 1 and 4. If the dynamos are worked 
























ST RIDS DISTRIBUTION. 


401 


fully up to their capacity, an extra allowance of copper must evi¬ 
dently be provided in this part of the circuit. It will often happen, 
however, that there is sufficient spare voltage, or the extra pressure 
may be obtained by a slight increase in speed, so that no extra cop¬ 
per is needed. In the case in point, No. 6 wire was used throughout 
the entire circuits, and proved entirely successful. 

520. W here the station load can be subdivided into three parts, 
operating at different times in the 24 hours, and geographically so 
located as to be separable one from the other, the arrangement 
shown in big. 221 effects a reduction in line material. Under these 
circumstances continuous service is given on line A, day service on 

*— 

*— 


lines A and B, and night service on lines A and C, thereby saving 
one-half the copper that would be called for by three independent 
circuits. A switch introduced at S serves to isolate line C, in order 
to protect the trimmers. 

521. Division 2, Constant Current Circuits , Embracing Generators 
and Receivers at Varying Distances from each other, has as yet re¬ 
ceived little or no practical development. Several attempts have 
been made to introduce the series system upon electric railways ; 
but so far the practical difficulties have been found commercially 
insurmountable, and the attempts have been abandoned. 

Divisions 3 and 4 of the classification of circuits on page 373, 
treating of constant potential circuits, covering at present the most 
important electrical plants, will be considered in a succeeding chapter. 


CITY COMMERCIAL LIGHTS (NIGHT ONLY) 


C — X X —*-*-K-X- ¥ -*■ 


-*■ 


-*—¥ -*— X- 

S 


-x- 


COMMERCIAL LAMPS AND MOTORS (DAY ONLY) 

-*-*-e--a-*- 


-X- 


B-*- 

CONTINUOUS SERVICE LAMPS AND MOTORS (DAY AND NIGHT) 

Ah*— X - □ -*-x-X-B-*-B-^— 


Fig. 221. Arc-Lamp Circuit. 


-*■ 


-X- 








402 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


CHAPTER X. 

PARALLEL DISTRIBUTION. 

Art. 522. The Evolution of the Parallel System. — In the dis¬ 
cussion upon series distribution, in Chapter IX., it has been shown 
that the development and extension of this method are limited in 
several directions. As the current in a series system is constant 
throughout the entire circuit, a variation in the number of customers, 
or in the amounts of energy supplied to respective customers, can 
only be obtained by a corresponding variation in the potential of the 
system. Every additional receiver increases the tension proportion¬ 
ally to the amount of energy recpiired to supply the additional 
demand; and the practical limit of possible difference of potential is 
reached, when a comparatively small number of translating devices 
have been placed upon the circuit. Experience has, thus far, demon¬ 
strated the inadvisability of increasing the potential of direct current 
circuits beyond 4,000 or 5,000 volts. Occasionally installations have 
been operated as high as 10,000 volts ; and though the tendency is 
toward higher pressure, such tensions require more careful and con¬ 
stant supervision and maintenance, and the gravity of injury arising 
from an accidental short-circuit is very largely increased. Again, 
the series circuit finds itself at a disadvantage when widely different 
amounts of energy are desired by various consumers along the line. 
As the quantity of energy to be delivered to each customer can only 
be varied by changing the potential between the terminals of the 
translating devices supplying the different subscribers, a customer 
using a large amount of energy must, necessarily, receive mains hav¬ 
ing great difference of potential. This has always been found to be 
a source of difficulty and danger; experience having shown the haz¬ 
ard to the community at large of introducing high potential circuits 
directly into residences, or the places of business, of the subscribers, 
where they are likely to be under the management of those little 
skilled in electrical manipulation. In order to attain any reasonable 
degree of economy, it has been shown that the load upon a series 


PARALLEL DISTRIBUTION. 


403 


circuit must be nearly constant and uniform throughout the whole 
time that the circuit operates, and that a series plant becomes decid¬ 
edly uneconomical when applied to the service of customers demand¬ 
ing widely varying supplies of energy, extending over different 
periods of time. In the development of electrical industries, central 
stations soon reached a sufficient magnitude to bring the limitations 
of the series circuit into sharp conflict with desired business exten¬ 
sions. To enable the central station to supply a large number of 
customers, without introducing potentials that are impracticable, the 
first step in electrical evolution was to equip the station with a num¬ 
ber of generators, each one of which was arranged to operate upon a 
separate and independent circuit. By this means dangerous poten¬ 
tials were avoided ; but still all of the individual circuits were open to 
the remaining objections of the series method, and the large number 
of independent machines proved decidedly expensive in operation. 
The multiplicity of circuits soon became confusing, and much dupli¬ 
cation of wire was necessary in order to cover a reasonable amount 
of territory. To improve the economy of the station, large dynamos 
were planned, capable of supplying a number of different circuits, 
upon each one of which the various receivers were placed in series. 
Such an arrangement is indicated in Fig. 222. 

523. It should be noted, in the examination of all the illustra¬ 
tions giving diagrammatically the outlines of various circuits, that the 
sketches serve merely to illustrate the principles of the circuit, with¬ 
out having special reference to the kind of receivers, or translating 
devices, which may be employed upon installations of differing design. 
Though the multiplication of circuits from one machine formed a step 
in advance, enabling the station to operate somewhat more flexibly 
and economically than the single series circuit, as indicated in Fig. 
222, in so far as losses in the dynamos themselves were concerned, 
it in no wise obviated the other limitations to which the series cir¬ 
cuit is subjected. As each of the series circuits from the generator 
is supplied with the requisite number of receivers to exhaust the 
potential of the dynamo, the tension of the system may, evidently, be 
reduced to any desired safe and practical limits, by multiplying the 
number of circuits, and proportionally reducing the number of re¬ 
ceivers which are placed upon each one. Another advantage accrues 
from the ability to arrange the differing circuits in such a manner that 


404 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


they may be thrown in and out of commission, in a way to allow a 
much greater variation of the load upon the station. In the case of 
an electric lighting plant intended to supply both municipal and com¬ 
mercial arcs, it. is feasible to arrange a multiple circuit generator of 
sufficient capacity to supply the current required for both circuits, 
placing all the municipal arcs upon one, and all the commercial lights 
upon the other. The two circuits would thus be entirely separate 
and independent of each other, and could be operated during differ- 







Fig. 222. Contrast between Plain Series and Series Multiple Systems. 


ent times of the day with essentially the same economy, so far as the 
losses in the circuit were concerned, as would accrue provided all 
the lamps were placed upon a single line. While this method intro¬ 
duces economy in the series system so far as the circuit losses are 
concerned, unless the generator be worked for a greater proportion 
of the time at its full load, the dynamo losses tend, to a considerable 
extent, to counterbalance the economy gained. While this method 
presents a partial solution of the problem, it in no wise provides any 








































































































PAR ALL EL D IS TRIP UTLON. 


405 


ability to deliver to the different customers varying amounts of 
energy, or to render the various customers independent of each other, 
in order that they may throw in and out of service, at pleasure, their 
receivers. This is really the most important disability of the series 
circuit. 

524. If the multiplication of separate circuits should be carried 
to its limit, each receiver would be supplied with a separate and inde¬ 
pendent wire from the generating-station, as shown in Fig. 223, and 
then all the chief objections to the series circuit disappear. In this 
vase the potential of the generating-station is reduced to the highest 
pressure required by any receiver that may be placed in service. As 
each receiver is supplied with a separate and independent circuit 
extended from the receiver to the generating-station, every translat¬ 



ing device is entirely independent from every other one, and may be 
thrown in or out of the circuit, without interfering in the slightest 
with the service of any other consumer. 

525. From the independence of the individual circuits, the 
amounts of energy supplied to the different receivers may be varied, 
by varying the quantity of current, without changing the pressure of 
any of the circuits. Thus, any subscriber may be supplied with any 
desired number of translating devices of different powers, and the 
amount of energy supplied varied at pleasure, by varying the quantity 
of current entering each translating device. As the various receivers 
may be adjusted to work upon any convenient electrical pressure, the 
circuits can be easily designed to never exceed safe limits ; and by 
increasing the quantity of current supplied by the station, it becomes 
possible to distribute energy over a very large territory and to a great 


/ 
























406 THE ELECTRICAL TRANSMISSION OF ENERGY. 

I 

number of customers. The independence of the receivers also allows 
the customers to throw their loads on and off at jdeasure, or to vary 
them to any extent. It is now evident that all receivers, instead of 
operating under a constant current and a varying pressure, operate 
under a constant pressure and a varying amount of current. The evo¬ 
lution, therefore, of electrical distribution has, evidently, taken place 
by a differentiation of the series method, the early single circuit being 
finally split up into such a number of parts as will practically give an 
independent line to each of the respective customers. To serve a 
large territory, however, by actually giving to each customer a circuit 



completely his own, extending from his receiver back to the generating- 
station, would introduce such complexities of wiring as to prohibit the 
introduction of this plan in installations of any magnitude. To avoid 
this objection, the next step consisted in uniting the adjacent re¬ 
ceivers into bunches, the various groups being placed in parallel to 
each other across the line, the system finally developing into the plan 
indicated in Fig. 224, in which the essential independence of the 
individual receiver is manifest. From the characteristic parallelism 
of the individual receiver circuits, the system has derived its name of 
the “Parallel” or “Multiple Arc System.” 

526. Methods of Distribution. — The arrangement whereby 
each translating device is supplied with an entirely independent cir- 










































































































PA RALLEL BIS TRIP UTION. 


40T 


cuit, extending from the generator to the receiver, gives the individ¬ 
ual customer the best possible service and the greatest independence. 
As each receiver is absolutely separate from every other one in the 
entire installation, it may be thrown on or off the circuit, or the 
amount of energy absorbed varied, without affecting in the slightest 
degree any other customers. With the individual -circuit arrange¬ 
ment, provided the speed of the generator at the station be main¬ 
tained constant, and the dynamo is not overloaded, the service 
delivered to all of the customers will attain the greatest uniformity. 
The inconvenience of this method, giving rise, in stations supplying 
a large number of customers, to utterly impracticable multiplication 
and complexity of circuits, has been noted, and the method of obvi¬ 
ating this, by uniting the various receivers into groups, and placing 
them in parallel across a common set of conductors, indicated. A 
difficulty here arises from the fact that the fall of potential along the 
conductors is not only a function of the resistance of the mains, and 
so an inseparable concomitant of the distance of the various custom¬ 
ers from the station, but is also a function of the amount of current 
which, at the time being, is passing through the mains. Thus, 
referring to Fig. 224, and assuming the plant represented to be a 
lighting circuit, the current at A will be much greater when all of 
the lamps are in operation than when the group at C only is in ser¬ 
vice. As the fall of potential depends, not only on the resistance of 
AC, but also upon the amount of current flowing through the mains, 
the decrease in the pressure at A will be much greater when all of 
the lamps at A, B, and C are lighted, than when a single group is 
alone in service. On the supposition that the generator always pro¬ 
duces a constant potential, if the mains are so calculated as to give B 
precisely the required tension, when all the lamps are in service, the 
pressure at B will be too high when A and C are extinguished ; or, if 
the mains are calculated so as to give the required tension at B when 
the other lamps are extinguished, if A and C are in service, the ten¬ 
sion at B will be too low, and the lamps will not burn with their 
required brilliancy. To obviate this difficulty, many systems of 
wiring have been devised, all of which may be finally reduced to 
four elementary forms. Before giving the fundamental systems the 
necessary careful consideration, it is advisable to review hastily the 
various plans of wiring. The ordinary features of the parallel system 



408 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


are exemplified in Figs. 224 and 225. From the generator two or more 
sets of mains are extended through the district to be served, the 
various receivers being placed in bunches across the mains, as indi¬ 
cated in the illustrations. A very slight consideration of the dia¬ 
grams will show that the electrical distance from the generator to 
the various receivers varies with the successive translating devices, 
and that the simple fact of the variation in distance from the receivers 
to the generator would preclude the possibility of supplying a uni¬ 
form pressure throughout the entire system. Evidently the electri¬ 
cal distance from the generator to the group A, Fig. 224, is much 
less than it is from the generator to the groups B and C. As there 
is no known substance which may be employed for the conducting 



system having no resistance, it is impossible on this account to 
render the pressure at A the same as it is at B and C. 

527. The Loop System. — The loop system is an endeavor to 
so design the conducting circuit as to render the electrical distance 
from the generator to each of the receivers the same throughout the 
entire circuit. 

Thus, in Fig. 226, one of the conducting leads aa', from the 
generator A, extends directly away from the dynamo to the end of 
the system, having the receivers placed in succession along its length. 
The main BC$, on the contrary, extends from the generator to the 
most remote point of the circuit b', without being attached to any of 
the receivers. At the point b ' it returns upon itself, toward the gen¬ 
erator, having upon this branch the connections to all of the receiv- 


















































PARALLEL DISTRIBUTION. 


409 



Fig. 228. The Tree System Fig. 229. The Closet System. 




































































































410 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


ers. An inspection of the diagram will show that, under these 
circumstances, the distance from the pole A of the generator to the 
pole B, throughout any of the translating devices, is precisely the 
same ; so the pressure in all of the receivers is not affected by their 
proximity pr remoteness from the generating-station ; and were it not 
that the fall of pressure is a function of the amount of current flow¬ 
ing, the receivers would always obtain a constant potential. 

528. The Spiral Loop. — Another loop arrangement is indi¬ 
cated in Fig. 227, in which the parallel conductors, A and B, are 
extended in the arcs of spirals from the generating-station through¬ 
out the territory to be served, both spiral arcs extending from one 
pole of the generator nearly to the other pole. In both of the loop 
systems the amount of material required for the conducting system 
is considerably increased, with, however, the advantage of much 
greater constancy in the electrical pressure delivered to the 
receivers. 

529. The Tree System. — Nearly all of the earlier installations 
upon the parallel system were laid out upon the so-called “ Tree 
System,” indicated in Fig. 228. The origin of the name is made 
quite evident by the illustration, from which it will appear that the 
main conductors in the system resemble a tree trunk, from which 
the auxiliary leads branch in various directions, quite after the 
fashion of a spreading tree, the receivers occupying the places of 
the twigs, leaves, and fruit. As the fall of pressure throughout the 
installation is augmented by the varying electrical distance of the 
receivers from the source of supply, the plan is, in this respect, 
defective. 

530. The Closet System. — The “Closet System” was an at¬ 
tempt to minimize the effect of electrical distance by collecting the 
various receivers into groups, each one of which was supplied with a 
separate and independent circuit back to the generating-station. 
This design is indicated in Fig. 229, the receivers being collected 
into four groups, those of each bunch equally placed in a circle around 
a center of distribution. From each distributing center, a set of leads 
is carried back to the generating-station, thus rendering each group 
independent of the other groups. This method is chiefly used in 
interior wiring, and may have formed the basis for the development 
of the famous “ Feeder and Main System,” to which detailed refer- 



PARALLEL DISTRLBUTLON. 


411 


ence will be shortly made. The detail of a single group, in the 
Closet System, is given in Fig. 230. Here the receivers are placed 
in a cncle around two circular mains, which receive their special 
circuit to the generating-station at two points diametrically opposite 
each other. A little consideration of the diagram indicates that the 
electiical distance of all of the receivers, with reference to the attach¬ 
ments of the feeding circuits, is the same. 

531. Conical Conductors. — Referring to Figs. 224 and 225, 
it is evident that the greatest current in the conductors occurs in 
the section immediately between the generator and that of the first 
consumer ; and as the distance from the station increases, thus pla¬ 
cing more and more consumers be¬ 
tween the station and the point of 
the mains under consideration, the 
current in the conductors decreases 
in direct proportion to the number of 
receivers that lie towards the station. 

It needs but little consideration to 
perceive that, if the cross-section of 
the mains is kept constant through¬ 
out the entire system, the conducting 
material in the circuit is not disposed 
to the best advantage. Either the 
current density near the station is 
too great, and the mains are in danger of becoming overheated, or, at 
the more remote portions of the systems, the current density is too 
small, and the conducting material is wasted. To proportion the mains 
to attain a constant current density throughout the entire system is 
evidently the remedy. Such an arrangement, when carried to the 
limit, would produce a conical conductor having the greatest cross- 
section at the station, and gradually tapering to zero at the extrer ity 
of the system. Under such a design, the rate of fall of the potential, 
due to the resistance of the conductors, evidently becomes much 
more uniform throughout the entire length of the circuit. Such an 
arrangement of conductors is indicated in Fig. 231. 

532. Another attempt to equalize pressure throughout the 
system has resulted in the employment of two conical conductors, so 
placed that the apex of one of the conductors is connected to one 



Fig. 230. 

The Closet System, Detail of Group. 


412 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


of the poles of the generator, while the base of the other conductor 
is connected to the other pole. Such an arrangement is shown in 
Fig. 232. 

Though this plan tends to equalize the total resistance of the 
conductors to the receivers from pole to pole of the generator, it 
produces quite an unequal variation in the “drop” to which the 
various receivers are subjected. The resistance of AB is less than 



CD, though the current is the same in both. Hence there will be 
more drop in CD than in AB, and of the total drop due to conductor 
resistance a greater proportion will occur in CD than in AB. 

533; Anti-Parallel Feeding. — In the diagram of the loop 
system, Fig. 226, one conductor, in extending away from the station, 
ran to the extremity of the line and then returned upon itself. A 
modification of the loop system is shown in Fig. 233, in which this 
extension of the conductor is split between both mains. In this 



illustration the current enters the mains at opposite extremities, 
flowing in reverse directions through the two conductors. Such a 
method is termed “Anti-Parallel Feeding,” and, as is shortly to be 
shown, is attended with some considerable advantage. 

534. The Distribution of Potential. — Satisfactory service in 
all systems operating under the parallel method can only be accom¬ 
plished by preserving, under all conditions of loading, an essentially 
constant pressure throughout the entire circuit of conductors. Theo¬ 
retically, the pressure at the terminals of all the translating devices, 














PARALLEL DISTRIBUTION. 


418 


be they what they may, should be perfectly uniform at ail times and 
under all conditions of loading, whether the load be that on the 
translating device in question or that of the entire system. Practi¬ 
cally, under no circumstances is it possible to attain an exact equality 
in the electrical pressure under all conditions. To reach this result 
in even a manner to secure satisfactory service, requires, with the 
best exercise of the greatest skill in proportioning, an expenditure of 
enormous amounts of copper in the conducting system. All of the 
forms of wiring may be reduced to four elementary forms ; and, 
therefore, a very careful consideration of the distribution of potential 
through each of these elementary forms, becomes a matter of prime 



importance to the successful designer of a parallel system. In order 
to simplify this investigation, the four primary forms of wiring may 
be classified as follows : — 

First. Cylindrical conductors, parallel feeding. 

Second. Conical conductors, parallel feeding. 

Third. Cylindrical conductors, anti-parallel feeding. 

Fourth. Conical conductors, anti-parallel feeding. 

To further simplify investigation, let it be assumed in all of the 
four cases now to be considered, that the conductors are two straight 
lines, supplied with an indefinite number of receivers, uniformly and 
equally distributed along the entire length of the conductors, each 
receiver taking the same amount of current, which is equivalent to 
assuming that the current supplied by the station flows between the 























414 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


two mains in a thin, uniform sheet, extending from end to end of 
the conductors. Such an assumption has a mechanical analogy in 
the replacement of a set of steps by an inclined plane having the 
same pitch. The load on the mains, in this connection, is supposed 
to be a constant one and uniform. 

Case I. — Cylindrical Conductors — Parallel Feeding. 

535. In Fig. 234, let AB and CD be the two parallel cylindrical 
conductors connected to the source of supply at A and C, the current 
flowing in the direction of the arrows. 



> * 

1 

o 1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

? 

1 

1 

1 

1 

1 

1 

1 

1 

1 

< I 

B 

■■mail in 

c 

-lo 

1 

p c 

\ 

1 * 

p ^ 

V 

) ( 

) 6 

C -- -C D 


-b 


Fig. 234. Diagram of Potential Distribution in Case I. 


Let L be the length of the mains in any desired units ; 

I 0 and — / 0 the currents at the station in each main , 
i and — i' the currents at any point x in each main ; 

V 0 and v 0 be the potentials at the station assumed to be constant; 
V' and d be the potentials at any point distant x units from the 
station, then, 

V 0 — v 0 = u 0 , the difference of potential between the mains at the 
station. 

Also V' — v' = ?/, the difference at any point x ; then, 

u 0 — u' = the fall of potential or drop between the station and 
point x. 

Let R = the resistance of each main per unit of length. 





















PARALLEL DISTRIBUTION. 


415 


Consider an element of the conductor dx at the point a'. By 
hypothesis, the current decreases regularly from I 0 at the point A, to 
0 at the point B, the extremity of the mains. Hence, in each ele¬ 
ment of the conductor AB, along its entire length, an elementary 
amount of current will pass from this conductor to the other main. 
As, by hypothesis, the rate of flow between the mains is uniform, 
// L will be the rate of flow from one conductor to the other con¬ 
ductor. At any point x, the current in the mains will be the total 
current at the station, minus all the current which has been trans¬ 
ferred across from one main to the other, between the station and 
the point ,r under consideration. 

The resistance of the element of conductor dx is Rdx. By Ohm’s 
Law, the variation of potential in any conductor is E = RI ; hence, 
in the two mains — 


d ( u 0 — u') = Rdx X 2 



(195) 


arranging, 


d{u 0 - »') =2 RI 0 {\ 



Integrating between x — 0 and x = L, — 





U 0 — U 


(2 L - x). 
L y 


(196) 


This equation represents a branch of a parabola to which the 
conductor is an asymptote. When x = 0, u 0 — u' = 0, showing no 
drop at the origin ; when x = L, n 0 — id = RI 0 L. To find the max¬ 
imum drop, — 

d (u 0 u ) 9 jp r 

-- ■ — w J 0 

dx 



(197) 


d 2 (u 0 — it) 
dx 2 


2 RI 0 \ 


or u _ u ' is a maximum when x = L (198), with a value of RI 0 L. 
536. Take an example. Suppose, in Fig. 234, — 


I 0 = 12 amperes. 

L — 60 feet. 

R = .02 co per foot. 

u 0 — u' 


Vo - V 0 = 40. 

/ RRx, 9 j v 

U 0 — U — -2. (J L — X). 


.02 X 12* 


X (120 - x). 


60 









416 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Let x be successively 10, 20, 30, 40, 50, and 60, then — 

.02 X 12 


60 

.02 X 12 
60 

.02 X 12 
60 

.02 X 12 
60 

.02 X 12 
60 

.02 X 12 
60 


X 10 X (120 — 10) = 4.4; 
X 20 X (120 — 20) = 8.0 ; 
X 30 X (120 - 30) = 10.8; 
X 40 X (120 - 40) = 12.8; 
X 50 X (120 — 50) = 14.0; 
X 60 X (120 — 60) = 14.4. 


537. From these values, the curve AB in Fig. 234 is plotted. 
A very slight consideration of this curve indicates a very unequal 
drop along the conductors, evidently due to varying current density 
per unit of cross-section in the mains. For incandescent lighting 
circuits, it is possible to compensate to some extent for this inequal¬ 
ity, by placing lamps of different voltage across the main, the higher 
voltage lamps being located nearer the source of supply. While 
almost any desired voltage of lamp may be quite readily obtained, 
yet to assume this method of compensation introduces a very unde¬ 
sirable maintenance complexity into the service. Furthermore, the 
slightest inspection indicates that the conducting material is badly 
disposed in reference to the load on the mains. Either that portion 
of the conductors nearest the station is too heavily loaded, and dan¬ 
gerously near the heating limit, or at the extremities of the mains 
there is too much copper, and economy may be introduced in original 
capital outlay by a reduction in the cross-section. To assume a safe 
current density per unit of cross-section, and then to construct the 
main to realize at all points this density, leads to a much more effec¬ 
tive disposition of the conducting material. This is accomplished by 
a tapering conductor, the cross-section of which varies directly with 
the current. 


Case II. — Conical Conductors — Parallel Feeding. 

538. In Fig. 235, let AB and CD be two parallel conical conduc¬ 
tors connected to the station at A and C, and having a cross-section 
constantly decreasing in proportion to the diminution of the current, 








PARALLEL DISTRIBUTION,\ 


417 


so that the current density shall be constant at all cross-sections. 
Assume the notation as indicated in Case I., with the exception of 
the symbol R, which in Case I. had a constant value per unit of 
length, while in the present case the value of R will evidently vary 
with the distance from the generating-station. In Case I., R was the 
resistance per unit of length of each main ; in the present conditions 




R will vary with x, and is the resistance of a unit of length at the 
point x only ; therefore, for R substitute r, denoting a variable resist¬ 


ance, — 


d {ii 0 — u') — rdx X 



(199) 


in which r is the resistance per unit of length at x. But r=p/S at 
any point x, p being the specific resistance and 5 the section of the 
conductor, then, — 

d («„ - «') = P -Ex 2 



L 




( 200 ) 






















418 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


arranging, 


but, 





5 



is the current density per unit of cross-section, which by hypothesis is 
constant; hence, integrating, — 

u 0 —u' = 2 R 0 I 0 x, (201) 

R 0 being the resistance per unit of length at the origin. 

This is the equation of a straight line, indicating a uniform drop 
from the station to the end of the conducting system, u 0 — u 1 being a 
maximum when x = L. 

539. Assuming the data in the example given in Case I., 
u 0 — n' = 28.8 volts, and the curve EG (see Fig. 235) is obtained, 
showing that, with a conical conductor having the same unit resist¬ 
ance at the origin as a cylindrical one, there is twice the drop; but, 
however, the weight of copper used in each main is only one-third of 
that employed in the cylindrical mains. This is evident from the 
fact that, in both systems the diameter at the origin and the length 
are the same, while the weights are in the same proportion as the 
volume of a cylinder and cone having the same base and altitude, or 
as one to three. If in the conical system the same weight of copper 
is allowed as in the cylindrical, the relative drop in the two systems 
is reduced in the proportion of two to three, as indicated in Fig. 235 
by the curve EF. The section of the conductors at the origin is 
then three times as great as in the cylindrical system. Thus, for the 
same cost of conducting system, the variation in potential may be 
decreased and the drop rendered more uniform by this method. 


Case III. — Cylindrical Conductors — Anti-Parallel Feeding. 

\ 

540. In Cases I. and II., the adjacent ends of the mains A and C 
are connected to the generator, the path of the current being out¬ 
ward away from the stations along the main AB, and backward 
toward the station through CD. Thus the direction of the current 
in AB is opposite to the direction of the current in CD. It is some¬ 
times feasible to connect the opposite ends of the main to the station 






PARALLEL DISTRIBUTION. 


419 


instead of the adjacent ends. Such a disposition is shown in Fig. 236, 
A being connected to one pole of the generator, and D to the other, 
the path of the current, as indicated by the arrows, being in the same 
direction in both mains. In this case an examination of the diagram 
shows that no receiver can enjoy the full difference of potential sup¬ 
plied by the generating-station, for the reason that V 0 is at one end 
of one main, and v 0 at the opposite end of the other. In this case 
u 0 — n °t th e potential throughout the entire length of 

both conductors, but is the variation between the different receivers, 
and is less than the total fall for the two mains by the amount lost in 
either one of the conductors. 



-x- 



V n 


Fig. 236. Diagram of Distribution of Potential in Case III. 


A further study of the diagram will show that — 

d ( u 0 — u') = jR (i — i) dx, (202) 

i and i' being the current in the respective mains at the point x. 


Integrating 



(203) 

(204) 





















420 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


This equation is also that of a parabola; but the vertex is at the 
center of the mains, and the maximum variation is one-half that of 
Case I. When x — 0 and x = L, u 0 — u' is 0, showing that at each 
end the receivers are operating under the same potential. To locate 
the maximum difference of potential between the receivers, — 


d\ ^—- ) = RL ( 1 


— ^ ) = 0 
x — 0 ; 


dx 


RI 0 - 


2 RL 


L 

x = L / 2, 


(205) 


a maximum ; hence, the greatest drop is at the center of the main, 
and has the value RI 0 L / 4. 

541. Taking the same value for the constants and variables as 
was assumed in the example in Case I., the curve CD plotted in Fig. 
286 is obtained. 

This curve shows the rate of variation in pressure between the 
various receivers along the mains, and does not indicate the entire 
drop between the potential of the generator and the point of least 
pressure in the conductor; for, as has already been indicated, the 
value of n 0 — n' is less than the total difference of potential by a 
quantity equal to the fall in pressure in one-half of the conducting 
system. The curve of total fall of potential may be obtained by 
decreasing the ordinates of CD by a quantity equal to RI 0 L / 2, 
which is the resistance of half the conducting system, and is repre¬ 
sented in Fig. 286 by the curve C'D'. Comparing these curves with 
Cases I. and II., a much more uniform and regular service to the 
customers is indicated, demonstrating the advantageousness of this 
method of wiring in cases where it is possible to employ it. 


Case IV. — Conical Conductors — Anti-Parallel Feeding. 

542. The plan of feeding from the opposite ends of the mains 
may be applied in conical conductors with equal advantage. The 
arrangement is shown in Fig. 237. From the equations in Cases II. 

and III., j (# o — u ') — (ri — rV') Ex, (206) 

r and r' and i and i l being the resistances and currents in either 
main, respectively, at the point x. Hence, by a similar train of rea¬ 
soning as in the previous cases, r = pi / 5, and r' = pi' / S' ; but 








PA PA LLEL D IS TP IB UTION. 


421 


p? / S and pi j S are constants for each main, by hypothesis; 
hence, — 

u 0 -u' = a constant. But u 0 - u' is here, as in Case III., the differ¬ 
ence in pressure between the receivers ; hence,_ 

v ' ~ v r = K — v n = V 0 - Vo - R 0 I 0 L ; (208) 

integrating (207) „ 0 -«' = R 0 J 0 L. (209) 

543. This is the equation of a straight parallel to the axis of ar; 
hence, by this method of wiring, there is no pressure variation be¬ 
tween the different receivers, all being submitted to precisely the 
same difference of potential. This method, then, presents an ideal 


H 


-I 


J 


K 


- 


A 

V 0 « 


12 



Fig. 237. Diagram of Distribution of Potential in Case IV. 


solution of constant pressure distribution. The only variation to 
which the receivers are subjected is that due to a change in the 
loading of the entire system, which may be compensated for by the 
methods of regulation to be described later on. The same conclu¬ 
sions as to the relations of the amount of drop and weight of copper 
in the conducting system may be applied in this case as in Case II. 

544. Collecting the curves indicated by-these equations, and re¬ 
ferring them to a single set of axes, a diagram is obtained as indi¬ 
cated in Fig. 238, from which a glance will show the relative potential 
distribution occurring in the four elementary systems. The four 
equations from which these curves are deduced are also here col¬ 
lected in a group, in order that their properties may be readily 
scanned. The salient deductions from these equations are collected 
in Table No. 51, in order to render them more conspicuous. 























O I 


422 


THE ELECTRICAL TRANSMISSION OE ENERGY. 



545. Case I. u 0 - u' = (2 L — x). (210) 

Case II. u 0 — u' = 2 jR 0 / 0 x. ( 211 ) 

Case III. u 0 - u' = (Z — x). (212) 

Case IV. u 0 — u’ — R 0 I 0 L. (213) 

Table No. 51. 


Relations between Cases I., II., III., and IV. 


Case No. 

Design. 

% 

Drop between 
Receivers. 

Relative 

Weight. 

Relative Energy 
Expended. 

Greatest 

Drop between 
Receivers. 

Drop between 
Generator and 
Receiver at 
Highest Voltage. 

Drop between 
Generator and 
Receiver at 
Lowest Voltage. 

1 

2 

3 

4 

5 

6 

7 

8 

'• I 

Parallel Feeding .... 
Cylindrical Conductors . . 

2 

3 

2 

RLI 

0 

RLI 

„. { 

Parallel Feeding .... 
Conical Conductors . . . 

4 

1 

2 

2 RLI 

0 

2 RLI 

in. j 

Anti-Parallel Feeding . . 
Cylindrical Conductors . . 

1 

3 

3 

RIL 

4 

RLI 

2 

3 RLI 

4 

IV.) 

Anti-Parallel Feeding . . 
Conical Conductors . . . 

0 

1 

3 

0 

RLI 

RLI 























































PARALLEL DISTRIBUTION. 


423 


546. In this Table the diameter of the conductors at the genera¬ 
tor is the same in all cases. If the same weight of copper be allowed 
in all cases, the value in Cols. G and 8, Case II., and Cols. 7 and 8, 
Case IV., must be multiplied by 3 / 2 ; and the values in Col. 5, Cases 
II. and IV., divided by 2. 

In the fifth column of this Table, figures are given showing the 
amount of energy which is lost by transformation into heat, due to 
the resistance of the conductor under a condition of maximum load¬ 
ing. This column is calculated from the following equation : — 



2 


in which r is the resistance per unit of length at the point where the 
current in the main is i. Integrating, the quantity of energy lost in 
the cylindrical conductors is found to be — 


f RIL, (214) 

and for conical conductors — 

RIL. (215) 

547. This corresponds with the relation shown in the Table No. 
51. If it is allowable to use the same amount of metal in both con¬ 
ical and cylindrical conductors, the section nearest the station in 
conical mains may be made three times as large as that in the cylin¬ 
drical conductors. Under these circumstances, the receivers are 
subjected to a much less difference of potential, and, at the same 
time, the energy wasted in the conductors is reduced by one-half of 
the amount that would be lost in cylindrical conductors having the 
same amount of copper. From the preceding considerations, it is 
evident that wherever it is practicable, the conical conductor fed 
upon the anti-parallel system gives the most uniform and regular 
service, wastes the least amount of energy, and subjects the receivers 
to the smallest potential variation. Wherever practicable, therefore, 
this method should be adopted. 


MULTIPLE WIRE SYSTEMS. 

548. The Three-Wire System. — If it were feasible to success¬ 
fully manufacture incandescent lamps capable of operating under any 
desired voltage, it would be possible, by increasing the resistance of 
the lamps, to work central stations at higher potentials, and economize 
in the material employed in the conducting system. It has been 



424 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


shown that, if the available potential remains constant, the amount of 
energy distributed will vary directly as the current, and the amount 
of energy lost in the circuit as the square of the current. By increas¬ 
ing the pressure, more energy may be delivered, or a greater territory 
served, without increasing the losses in the circuit. So far, attempts 
to make incandescent lamps of much more than 200 ohms resistance 
have not been commercially successful; and for the standard 16 
candle-power lamp, an available difference of pressure at the lamp 
terminals of about 100 volts is all that can be rendered useful. Ex¬ 
perience has shown that a maximum variation in pressure throughout 
the conducting system of more than 10 per cent is not compatible 
with good service. Thus, the greatest difference in pressure at the 
generators, in the methods of wiring so far described, is limited to 
about 110 volts. Any plan which will render available a greater dif- 


A 



Fig. 239. Multiple Series System. 


ference of potential will introduce a notable economy in the cost of 
the conducting system. 

549. Suppose two conductors A and C, Fig. 239, between which 
is maintained a difference of potential double that which is necessary 
for any one of the receivers ; for example, 220 volts in an incan¬ 
descent lighting system of 110 volt lamps. It is then feasible to 
place lamps in series of two between the mains A and C. Therefore, 
for a given number of lamps, the necessary quantity of current is 
halved, and the admissible fall of potential may be doubled. The 
resistance of the conductors for a given output along the line may be 
quadrupled, and, consequently, the price of installation is reduced 
nearly 75 per cent. This device, however, involves the sacrifice of 
the independence of each receiver. As the receivers are placed in 
groups, each one involving a series of two, it is necessary to throw 
in or out of service an entire group ; for if a single receiver be placed 










PARALLEL DISTRIBUTION. 


425 


in service, it will receive double the pressure for which it was in¬ 
tended. This defect, however, may be obviated, by so designing the 
station machinery that the dynamos are operated in groups of two 
placed in series, to obtain the desired voltage, and then introducing a 
third wire B, as indicated in Fig. 240, which occupies a position inter¬ 
mediate between the two generators, and extends through the entire 
system of conductors. Under these circumstances, each ?///z7 in the 
station must consist of two generators, connected together in series. 
By inspection, it is evident that the middle wire is traversed by a 
current which is only equal to that originated by the difference in the 
number of receivers that are simultaneously in service on the two 
sides of the system. The principal, or outer conductors, when the 



whole plant is in service, only carry a current equal to one-half that 
which would be necessary to supply the same number of receivers if 
installed on the two-wire system ; and in this case, as the center wire 
is not traversed by any current, it has received the name of the 
“Neutral Wire.” 

550. Supposing now that a part of the load on one side of the 
system be thrown off. In the previous instance, both sides were bal¬ 
anced, but now one side needs more current than the other; and to 
preserve the independence of the individual receivers, the neutral 
wire acts as an overflow main, permitting the excess of current on 
the overloaded side of the system to return to the generator without 
affecting the other side. For example, in Fig. 240, suppose 100 
receivers to be in service between A and B, and 80 between B and C, 
























































426 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


each requiring one ampere ; 100 amperes will be needed on the AB 
side, and 80 on the BC side. 100 amperes will evidently pass out 
through A, 80 back through C, and 20 back through B. By this 
method it is practical to introduce very large economics in the cost 
of the conductors, to greatly extend the scope of the plant and the 
distance over which it is possible, from a financial standpoint, to 
transmit electrical energy. The copper saving which may, in this 
way, be practiced, is easy to calculate, and depends upon the rules 
which have already been given. Suppose that, for a given plant, a 
certain economical density of current has been determined. This 
value is independent of the method of distribution employed ; so if 
the same current density is to be used in the two systems, it will be 
observed that, by the three-wire method, the fall of potential is 
reduced to one-half. As an example, assume a current of 500 am¬ 
peres under a pressure of 110 volts to be required by the receivers, 
with a drop of 8 volts, and that the most advantageous current 
density is found to be 1000 amperes per square inch. It is neces¬ 
sary then to employ for two-wire system conductors .5 in area, each 
giving rise in the length of the conducting system to a drop of about 
7J percent of the total available potential. Adopting the three-wire 
system for the same case, as the potential is doubled, the same 
amount of energy is delivered with half the current, and so the cur¬ 
rent of the outer conductors is reduced to 250 amperes, and, at the 
same current density, the amount of copper is reduced in each con¬ 
ductor to .25 sq.’ in. in area. It is a common practice to make the 
third wire equal in section to the principal conductors, then the total 
cross-section is .75 sq. in., instead of 1.00 sq. in., and the total amount 
of copper is reduced by one-fourth. The fall of potential, however, 
remains equal to 8 volts ; and, inasmuch as the total voltage is raised 
to 220, the percentage value of the fall potential is only 3.6 per cent 
instead of 71 per cent, as in the preceding example. If, on the con¬ 
trary, the calculations are based upon an equal percentage fall of 
potential in each case, the economy to be obtained in the amount of 
copper is evidently increased to five-eighths. Thus, in reality, each 
of the three conductors of this system may be reduced to one-fourth 
of the area necessary with the two-wire plan, the third wire being 
still assumed to be equal to the other two. Therefore, the total 
amount of copper in the three conductors is only three-eighths of that 


PARALLEL DISTRIBUTION. 


427 


which is required under the two-wire system to deliver the same 
amount of energy with the same percentage of drop. If all the re¬ 
ceivers on one side of the conducting system were out of service, 
while all on the other side were in commission, it is conceivable that 
the neutral wire would be called on to carry a current as great as 
that of the outer main. This can only happen by some accident, 
such as the blowing of a main fuse, which would actually open one of 
the outer conductors ; for by no possibility of service condition would 
half of the customers be out of service while the other half were 
in action. 

551. Good practice indicates the advisability of placing half of 
the receivers of each customer on one side of the system, and half 
on the other. Then, in the event of the opening of one conductor, 
one-half of all of the receivers that are in the circuit are thrown out; 
and under this condition the neutral wire can only be traversed by 



Fig. 241. Balancing Diagram. 


one-half the current of the outer main, and the relative amounts of 
copper for the two and three wire systems under such similar condi¬ 
tions are as sixteen to five. It is also feasible, by a careful study of 
the various consumers, to place across the outer conductors such 
of the receivers as are able to accommodate themselves to great 
changes in voltage, as motors, for example, or groups of lamps that 
are rarely in service. Moreover, the two halves of every important 
installation may always be arranged to make the demands of each 
part sensibly the same. This precaution prevents long portions of 
the neutral conductor from being traversed by a current of sensible 
amount that does no useful work, thus economizing the lost energy. 

552. The different parts of the third wire may be traversed by 
various amounts of current, both as to intensity and as to sign, 
although at the same time a balance of the whole system be care¬ 
fully preserved. Fig. 241 gives an illustration of this condition, from 
which it is obvious that on each side of the system the same number 








428 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


of lamps are in use, and that, while a part of the third wire is trav¬ 
ersed by a current equal to three lamps, the system, on the whole, is 
balanced, and the portion of the conductor nearer the station is en¬ 
tirely neutral. It is advisable to carefully study every important 
installation, and to arrange the distribution of currents to attain the 
maximum conductor and energy economy. 

553. Such are the advantages of the three-wire system. On the 
other hand, there are certain inconveniences, which it is now advis¬ 
able to consider. It must be noted that it is necessary to maintain 
in operation two dynamos, instead of a single machine ; and a station 
unit on the three-wire plan must consist of two dynamos, each having 
half of the power required on the two-wire plan. While the weight 
of the two dynamos for the same output will' not differ sensibly from 
that of a single machine, the initial cost, expense of operation, and 
loss of efficiency are increased. The apparatus at the central station 
becomes somewhat more complicated ; but this inconvenience is con¬ 
fined to the dynamos, for the engine, or other motor, may remain in 
each case the same. The driving machinery, such as shafting, pul¬ 
leys, etc., must be connected to two generators instead of one. Also, 
the difference of potential between the system and the ground is 
doubled, and the chances of accident due to failure of insulation be¬ 
come largely increased. These objections to the three-wire system 
are by no means comparable with the advantages and economy to be 
derived ; so all central stations of any importance are now, without 
hesitation, designed and laid out in accordance with the principles 
enunciated. Indeed, so great are the benefits, that the economical 
principles outlined have been extended, and similar systems using 
five and seven wires, with corresponding advantages, are by no means 
unique. 

554. Multiple-Series System and Modifications of the Three- 
Wire System. — In local installations of small extent, where the full 
plant load, or at least the greater part of it, is constantly on the cir¬ 
cuit, and where the independence of the individual receiver is not 
essential, it becomes possible to avoid the complexity introduced by 
the three-wire system, by operating the receivers in groups of two or 
more, placed upon circuits in parallel with each other, thus giving 
rise to the multiple-series method — see Fig. 289. The origin of 
the three-wire system was, doubtless, an effort to secure at once 


PARALLEL DISTRIBUTION. 


429 


the independence of each receiver, and the economy of high po¬ 
tential. 

In the multiple-series system, all the receivers of each group 
must be in operation at any one time ; as, if any one of the group is 
thrown out of service, the remainder will be either subjected to an 
electrical pressure greater than that for which they were designed, or 
idle resistance must be introduced in the circuit to absorb the energy 
previously consumed by the now isolated receiver. In this direction 
the multiple-series circuit labors under the same disadvantages and 
limitations as the ordinary plain-series circuit. 

It is possible in some cases, where the load on the system is a rea¬ 
sonably constant one, to simplify to some extent the three-wire system 
by avoiding the complexity of two dynamos at the central station. In 
Fig. 242 such an arrangement is indicated—a single dynamo sup¬ 
plying the circuit having double the electro-motive force of the receiv¬ 



ers on the sides A and B. The third wire still exists in the circuit, 
but does not return to the station, nor is any connection made with 
the generator. Under these circumstances, if any one of the receiv¬ 
ers in the group A be thrown out of commission, the circuit of none 
of the others will be actually opened, and, conseqntly, their operation 
will proceed uninterruptedly. As the generator produces a constant 
electro-motive force, and as now the resistance of the A group of 
receivers is increased by the opening of the circuit of one or more 
of them, and is higher than the resistance of the B group, the fall of 
potential throughout the system will be the same as when all the 
receivers were in operation, but the potential upon the A group will 
now be greater than that upon the B group. While formerly the 
potential of the central conductor cc was precisely midway between 
the potentials of the external conductors, the potential of cc is now 
not midway between those of the outer conductors, but approximates 
more nearly to that of the conductor B. In cases where such a 










430 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


variation in service can be tolerated, as in factories, or other com¬ 
mercial institutions operating their own lighting plants, this method 
approximates sufficiently toward the best service to be desirable. 

555. For very small installations, where the mains extend a con¬ 
siderable distance from the generator, yet where the load is so light 
as to render two machines inexpedient, the conductor economy of 

• the three-wire system may be rendered 
available by the device indicated in Fig. 

243. Here the generator is supplied 
with a third brush F', set midway be¬ 
tween the regular brushes, to which the 
third wire is attached. If the system is 
well balanced, with rarely any current in 
the neutral, this scheme is fairly suc¬ 
cessful ; otherwise, there is likely to be 
destructive sparking at the commutator. 

556. The three-wire system is sus¬ 
ceptible of a very great number of modi¬ 
fications, many of which will readily occur 
to the fertile designer. Mr. Leonard, in 
the Electrical Engineer, indicates several 
useful combinations, which are illustrated 
in Figs. 244, 245, and 246. 

In the arrangement outlined in Fig. 

244, a single dynamo is connected to the 
external conductors M and P, having an 
electro-motive force double that of the 
receivers to be placed upon the circuit. 
The third wire, instead of returning to 
the generator, is connected with the pole 
of the storage battery S, the other pole 
of which is in electrical communication 

with the main M. Under these circumstances, a current thrown 
upon the third wire N is absorbed by the storage battery, while the 
extra load upon the M side of the system is cared for by the output 
of current from the battery in question. 

557. In Fig. 245 an arrangement is indicated, consisting of two 
generators, A and B ; the A generator has double the potential of 

















































PARALLEL DISTRLBUTION. 


431 


all of the receivers, while the B dynamo is capable of developing an 
electrical pressure equal to that required by a single receiver. 

When the load on the P side of the system is greater than that 
on the M side, a current returning through the central conductor N 



Fig. 244. Three -Wire System with Storage Battery Equalizer. 

actuates the dynamo B, causing it to operate as a motor, and thus, 
by means of the counter shaft E, relieving the prime mover of a part 
of the load of the dynamo A. When, on the contrary, the M side of 
the system is overloaded, the dynamo B acts as a generator, sup¬ 
plying the necessary additional current. 



558. The design of Fig. 246 is a modification of the preceding 
arrangement, by means of which the generator A may be located at 
a considerable distance from the district to be served, while in close 
proximity to the district a motor R and generator C are located. 
The generator A may be run at a sufficiently high potential to make 
the loss between G and R comparatively small, while by means of 

































































432 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


the motor R the second generator C may be made to operate in 
conjunction with the generator A upon the three-wire system, as 
indicated in the previous design. 

559. The Five-Wire System. — By an extension of the princi¬ 
ples thus developed, a greater number of circuits may originate from 
the same station, giving rise to methods of multiple wire distribution, 
embracing five or even seven wires, operating at correspondingly 
high potentials, and enabling a corresponding reduction in the ex¬ 
pense of the conducting system. All of the advantages previously 
enumerated are augmented in proportion to the increase in the num¬ 
ber of wires, while, on the other hand, the objections inherent in the 
multiple wire systems present themselves with correspondingly in¬ 



creasing force. The greater the complexity of the station, and the 
difficulties of obtaining sufficient insulation for the higher potential 
differences have so far, in this country at least, prevented a very 
wide introduction of anything but the three-wire system. Nearly all 
of the plants of the Edison Company in this country are built upon 
the three-wire plan, and form the most notable, and the most thor¬ 
oughly designed and executed, examples of this method of distribu¬ 
tion. In Europe, on the contrary, where the areas to be covered are 
perhaps not so great as in America, and where greater care and more 
thorough work is to be expected from an older and more complete 
civilization, the five and seven wire systems have attained quite a 
wide introduction, accompanied with very notable success. 

560. In Fig. 24T are given diagrammatically the systems of 



































PARALLEL DLSTRLBUTLON. 


433 





some of the most extensive European systems of direct current 
distribution, being adopted in the following towns : — 

A. Parallel system, Berlin (Markgrafenstrasse Station), La Coruna. 

B. Parallel system with secondary batteries, Salzburg, Lyons, Toulon, 

Montpellier. 

C. Simple three-wire system, Berlin (Mauerstrasse Station, Schiffbauer- 

darnrn, and Spandauerstrasse), Elberfeld, Helsingborg, Malaga. 

D. Three-wire system with one dynamo and secondary batteries, Miil- 

hausen, Stockholm, Sundswall. 

E. Three-wire system using two dynamos, Vienna (Mariahilf), Darm¬ 

stadt, The Hague, Stettin, Breslau, Copenhagen. 

F. The five-wire system with equalizing dynamo, Trient. 

G. The five-wire system with equalizing dynamo and secondary batter¬ 

ies, Paris (Place Clichy). 

// The five-wire system with two generator dynamos, Vienna (Neubad). 










































































434 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


56 1 . The use of auxiliary dynamo machinery in several of these 
installations will be noticed. The method of employment is similar 
to that already indicated in Figs. 244, 245, and 246, for the three- 
wire system, and in Fig. 248, showing in detail the design for a five- 
wire system. Here the generator G runs at a potential sufficient 
for four receivers, and is attached to the two external mains of the 
system. At any desired intermediate point or points, three dynamo 
machines are introduced, each one operating at a potential equal to a 
single receiver. So long as the system is entirely balanced, the aux¬ 
iliary dynamos absorb merely sufficient power to turn their armatures 
against friction of the bearings and the slight losses due to internal 



Fig. 248. Five-Wire System with Motor-Dynamo. 


currents. In the case of any want of balance in any part of the sys¬ 
tem, the dynamo connected with that portion acts either as a motor 
or as a generator, depending upon whether the unbalancing is such as 
to give rise to a current flowing towards the station through the 
intermediate wire, or away from the station. In the first instance, 
the current flowing toward the station passes through the auxiliary 
dynamo, causing it to run as a motor, thus releasing the station of 
that amount of load. Contrariwise, should the unbalancing make 
the current flow away from the station in any intermediate wire, the 
dynamo acts as a generator, demanding from the station such an 
amount of power as will enable it to add to the circuit the required 
current. This subject will be further illustrated in the paragraphs 
upon motor transformers, in the succeeding chapter. 







































































PARALLEL DISTRIBUTION. 


435 


562. Relative Area Covered by Two, Three, and Five Wire 
Systems. — 1 he territory that can be served by a central station only, 
depends upon the amount of copper that is placed in the conducting 
system in proportion to the number of customers to be served. 
W ith a limited drop, the cost of the conducting system may, even in 
a small territory, rise to such an amount as to prevent the enterprise 
from being a commercial success. If a given receiver is to operate 
at a definite distance from the station under a predetermined drop, 
the weight of the conducting system is readily calculated. If the 
distance is increased M times, the drop remaining the same, the 
weight of the conducting system will be proportional to M 2 . In 
general, the weight and, consequently, approximately, the cost of the 
conducting system, is expressed by the formula — 

W = AI\ (216) 

in which W is the total weight of the circuit, A a constant embracing 
the drop, the conductor weight per customer, and the length of the 
system. With a drop of 5 per cent, and an average of 12^ lbs. of 
copper per lamp in the conducting system per 50 watt lamp, a single 
station on the two-wire system is limited to a radius of about 1600 ft. 
To extend the territory to 2300 ft., formula (216) indicates that an 
expenditure of 25 lbs. of copper per lamp is required. Table No. 52 
indicates the relative possible areas to be served, and weight of cop¬ 
per per lamp and drop. 

Table No. 52. 

Areas Covered by Multiple-Wire Systems. 


Kind of System. 

Radius of Profitable District with b % Drop. 

Copper 12i lbs. 
per 50 Watt Lamp. 

Copper 25 lbs. 
per 50 Watt Lamp. 

2-Wire System. 

1600 Feet. 

2300 Feet. 

2-Wire System Feeders and Mains . 

2500 Feet. 

3500 Feet. 

3-Wire System. 

2300 Feet. 

3500 Feet. 

3-Wire System Feeders and Mains . 

4000 Feet. 

6000 Feet. 

5-Wire System. 

5000 Feet. 

7200 Feet. 

5-Wire System Feeders and Mains . 

8200 Feet. 

12000 Feet. 


563. The Feeder and Main System. — All the methods for cir¬ 
cuit design thus far indicated may, analytically, be reduced to one of 
the four elementary cases. When applied to the distribution of very 
large amounts of electrical energy, extending over considerable areas, 











436 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


embracing points widely separated from each other, all of these 
methods, even including the multiple-wire systems, require the ex¬ 
penditure of so much material in the conducting system, in order to 
maintain a sufficiently uniform electrical pressure throughout the con¬ 
ducting network, as to make the cost of the system too great to per¬ 
mit of a profitable return upon the capital invested. As a solution 
of this problem, Mr. Edison, in this country, introduced the Feeder 
and Main System, which consists in subdividing the territory to be 
served into a large number of districts, by grouping the customers in 
proximity to each other into blocks located as near as possible at 
equal distances around a number of central points. From each of 
these radiating centers, receiving the name of Centers of Distribution, 
a pair of conductors, termed Feeders, is carried back to the central 
station. Upon the feeders no customers whatsoever are, under any 
circumstances, placed. From each of the centers of distribution 
there also extend a second set of mains running electrically away 
from the center of distribution, and so away from the central station, 
the office of which is to serve the various consumers. • 

564. This set of conductors has received the name of “ Distribut¬ 
ing Mains.” By this means the entire territory is split up into a 
number of subdivisions, each in the most direct electrical communi¬ 
cation with the station, by means of such an independent pair of 
conductors as will enable the station to supply the distributing center 
with the required amount of current, at any desired electrical pres¬ 
sure. Inasmuch as there are no customers upon the feeders, the fall 
of potential in the feeders is a matter of but little importance so far 
as the requirements of good service are concerned, these conductors 
being designed merely to supply to the distributing center the re¬ 
quired amount of current under the most economical conditions. 
The central station may embrace a number of different dynamos, all 
running at different electrical pressures, each one conveying to its 
appropriate center the necessary current, so adjusted that on arrival 
at the distributing center all of the currents will come in under a 
uniform pressure, maintaining the essential constant electrical poten¬ 
tial over the entire district. Such an arrangement is indicated dia- 
grammatically in Figs. 249, 250, and 251. 

In Fig. 249 the central station is shown at MN. From this 
point a pair of feeders MA, MA' extend to the center of distribution 


PARALLEL DISTRIBUTION. 


437 


AA'. Two other sets of feeders also extend to the centers CC and 
BB\ From AA', BB', and CC' the distributing mains are extended, 
across which the receivers are located. From M to A, B, and C any 
desired fall of potential may be allowed to take place in the feeders 
without in any way affecting the service of the respective receivers 
extended upon the distributing mains emanating from these points. 



The distributing mains, however, must be so designed that, with all 
variation of load which shall be thrown upon them, the fall of poten¬ 
tial shall be kept within such a limit as good service conditions 
require. 

565. A similar design is indicated in Fig. 250, in which the 
station is located at MN in the center of the district to be served, 



Fig. 250. Feeders and Mains. 

from which three sets of feeders, MA, MB, MC, and MA', MB', and 
MC', extend to the distributing mains, that are located in ellipses 
around the central station. As in the previous illustration, no re¬ 
ceivers are placed upon the feeders, so the variation in pressure in 
this part of the conducting circuit does not affect the customers, but 
may be made as great as the rules of maintenance, economy, and 





















438 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


safety dictate. Upon the distributing mains, A, B, C, and A', B', and 
C', the drop must be restrained within service limits, no matter at 
what sacrifice of conducting material. This design is much superior 
to that in the preceding illustration, as it is evident that each feeder 
can supply the distributing mains in two directions, thus shortening 
the electrical length of the distributing mains, and obviating accident 
in case of the rupture of any conductor. 

566. A still further improvement is indicated in Fig. 230, in 
which the distributing mains assume the form of a circle, around 


LINE OF BOULEVARDS 



which the receivers are equally spaced, while the feeders are intro¬ 
duced at two diametrically opposite points upon the circumference. 

567. For installations upon a large scale, such as are required 
by urban distributing plants, especially for incandescent lighting, all 
of the foregoing principles are usually combined in the design of the 
conducting system. An excellent example of this is indicated in 
Fig. 251, giving in a skeleton form the mains of the Edison Company 
along one section of the plant in Paris. A slight inspection of the 
diagram indicates that the general design of the conducting circuit is 
that of a three-wire system embracing conical conductors for the dis¬ 
tributing mains, with anti-parallel feeding, thus realizing the highest 






































PARALLEL DLSTRLBUTION. 


439 


economy in the conducting material, and the least possible potential 
variation. 

568. Location of the Central Station. — In the case of series 
distribution, it is shown that the location of the central station is a 
matter of relatively slight importance, provided the site is chosen on 
the perimeter of the polygon formed by the line of circuit; that all 
locations on this line are equally advantageous ; and that in case it 
is necessary to slightly depart from the actual location of the circuit, 
all points are equally available that are equally distant from the line. 
Under the parallel system the location of a central station becomes a 
matter of the most paramount importance ; for, under this system, 
the amount of current, and not the electrical pressure, is the govern¬ 
ing factor. 

The losses entailed by the conducting system vary as the square 
of the current flowing, and as the resistance of the conducting sys¬ 
tem ; and as the supply of a definite territory requires a definite cur¬ 
rent, the resistance remains as the only variable at the command of 
the engineer. The dictates of both maintenance and economy, and 
the requirements of good service, make it essential to reduce the ex¬ 
pense of the conductor system in every direction to the lowest possi¬ 
ble amount. As will be now shown, this is best accomplished by 
locating the central station at the electrical center of gravity of the 
district to be served, considered in relation to the various points to 
which energy must be distributed, and the amount of energy to be 
conveyed to each respective center. In many cases, the very impor¬ 
tant consideration of coal and water supply, the availability and econ¬ 
omy of real estate, and physical causes affecting the ability to obtain 
the requisite foundations for heavy machinery, must be taken into 
consideration in the selection of the station site. Leaving, for the 
present, these conditions out of the question, the location of the site 
should be determined, in so far as the relation to the conducting sys¬ 
tem is concerned, at such a point in the district as will place it at 
the electrical center of the conducting system. To properly locate 
the central station, a reasonably accurate map should be made of the 
district, with a careful canvass of all the probable customers, obtain¬ 
ing the amounts of energy that they are likely to demand. An 
inspection of a good map so prepared will enable the engineer to 
select a number of points in the district, which will, from the topo- 


440 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


graphical features of the territory, be made centers of distribution. 
From these centers of distribution the distributing mains extend, 
electrically speaking, away from the station, while toward the station 
from each point the feeders will run. From a canvass of the custom¬ 
ers, the amount of energy to be delivered at each of the centers of 
distribution is determined, thus giving the maximum current flowing 
through the feeders, and the current to be diffused by the distrib¬ 
uting mains. These amounts should be carefully noted opposite 
each of the centers of distribution, where the feeder joins the dis¬ 
tributing main. 

569. To determine the proper station site, suppose, in Fig. 252, 
the irregular outline includes the territory to be served, the black 
dots scattered throughout indicating the location of each of the 

centers of distribution, and the amount of cur¬ 
rent to be delivered at each of the respective 
points. The problem to be solved, in order to 
determine the proper location of the station, is 
to ascertain the electrical center of gravity of 
the points of distribution, precisely as the center 
of gravity of an irregular solid would be ob¬ 
tained. Graphically, a solution is obtained by 
selecting any two centers of distribution, and 
joining them by a straight line. 

This line should be divided into two parts, in¬ 
versely proportional to the amount of current to be delivered at 
each of the centers ; such a point is then electrically the center of 
gravity of the two distributing points in question. The process is 
repeated until the resultant center of gravity of all of the centers 
of distribution is obtained, indicating the best location for the sta¬ 
tion, considering simply maximum economy in the cost and main¬ 
tenance of the distributing system. Analytically, the determination 
of the station site is as follows : — 

Assume that at the points 1, 2, 3, etc., currents represented by 
z, z', z", etc., are to be delivered, and that the centers of distribu¬ 
tion may be connected by straight lines with the station. The 
weight of each conductor for a given fall of potential is propor¬ 
tional to the product of a constant depending upon the allowable 
drop, the current z, and the square of the length of the con- 


12 3 



Fig. 252. 

Diagram to Determine 
Location of Station. 





PARALLEL DISTRIBUTION. 


441 


ductor /. Hence, the weight of each conductor 01, 02, 03, etc., 
will be — 

w = Al\ (217) 


in which w is the weight of the conductor, and A the constant above 
referred to. The total weight of the feeder system is the sum of all 
these equations applied from the point O to the distributing points 


1, 2, 3, etc., — 


W=AZl 2 i. 



The study of mechanics presents a similar problem, the solution of 
which indicates a key to the solution of the above equation. 

If, at the points 1, 2, 3, etc., masses of matter are supposed to 
be concentrated, the magnitude of which may be represented by the 
current values i , i', i", etc., the term 2 l 2 i represents the moment of 
inertia of this system with reference to the point O, from which the 
following conclusions may be drawn : — 

570. First. The moment of inertia of the system, with refer¬ 
ence to the center of gravity, is a minimum. 

Second. The moment of inertia referred to any other point than 
the center of gravity, depends upon the distance “ D ” between the 
center of gravity and the second point of reference. The moment 
of inertia is equal upon all points of any circumference described 
with the center of gravity as a center with “ D" for a radius, there¬ 
fore — The best site for a central station is the electrical center of gravity 
of the centers of distribution. All locations equally distant from this 
point are equal in value. As the station is removed from the electri¬ 
cal center of gravity, the pounds of copper required for the conducting 
system are rapidly increased. 

571. Let W be the weight of copper required for the conductors, 
when the station is located at the electrical center of gravity of the 
system, and W' the weight when located at any point distant d feet 
from the center of gravity. 

Let l be the length of any feed. 

Let i be the current in this feed. 

Let L be the average length of all the feeds. 

Let I be the total current. 

Let the above symbols apply when the station is located at the 
electrical center of gravity, then, — 

2 Ti = Z 2 /; 

JV = A Id I, 


and 


(219) 

( 220 ) 


442 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


A being a constant depending on the allowable drop, as shown in the 
paragraph on the “ Limits of the Three-Wire System. If the station 
is moved to another site, distant d feet from the center of gravity, 
then,— 

Let V = the new length of any feed, 

Let L' = the average length of all the feeds, 

Let IV = the weight of copper now required, 

Let i and / remain the amounts of the current, as before; 

then, 2/' 2 / = Z' 2 /, (221) 

and W’ = AL' 2 I ; (222) 

from which IV' — IV = L’~ — Z 2 . 


The mean length is analogous to radius of gyration and, therefore, — 

L 2 - d* = L ' 2 ; IV'— W = Aid 2 • 

W' — W _ d 2 

and w L 2 • 

This is the equation of a parabola having its vertex at the origin and 
branching upward away from the axis of ar. So the conductor material 
increases very rapidly as the station is moved away from the electri¬ 
cal center of gravity of the system. Increasing the weight of the 
conducting system means not only a much larger initial investment, 
but also increased maintenance expense, and increased cost due to 
energy lost in the conducting system. 

572. On the other hand, the removal of the station from the 
center of gravity may permit the utilization of real estate at such 
an advantage as will more than compensate for the extra capital in¬ 
vested in the line. Furthermore, locations may be chosen permitting 
the utilization either of water-power directly, or of water to supply 
condensing engines, or may provide access to transportation facilities 
for fuel supply, thus cheapening the cost of power production to such 
an extent as to make the additional conductor investment required by 
the change in location a most desirable investment. The decision of 
the location should be determined from the following considerations : 
Determine the cost of plant, and cost of operation, with station located 
at the electrical center of gravity. Determine the value of the same 
items with the station placed at any other location presenting sup¬ 
posed advantages. An equation between these quantities will at 
once indicate which of the two sites possesses the greater advantages, 
and the relative value of the merits in both cases. 





PA RA LLEL D/S TRIE UTION. 


443 


573. Location of the Feeders and Centers of Distribution. — 

In the preceding analytical investigation, it has been assumed that 
the feeders extended to the centers of distribution in straight lines. 
In practice, this would rarely be the case, and the symbols in the 
equations must be assigned values obtained from the actual location 
of the conductors. Many other circumstances contribute to limit the 
number of feasible selections for the location of the central station, 
and the design for the main feeds. Regarding the points where the 
feeds unite and join the network of distributing mains, it is obvious 
that the possible theoretical locations are very much limited, and 
must conform to urban geography. 

Distributing boxes and other conduit structure must be located on 
the streets and at street corners ; and, therefore, for each block there 
can only be four possible locations from which to choose for the junc¬ 
tion between the main feeds and the distributing mains. Application 
of the equations, however, are available in determining which, of all 
possible locations, will be, on the whole, the most advantageous ; and 
the actual placing of the mains should conform, as nearly as possible, 
to that which is thus obtained. 

574. Distributing Mains. — It has been pointed out that the 
reason for employing the system of feeders and mains, is the neces¬ 
sity for preserving, at all points throughout the distributing mains, a 
constant difference of potential, in order to secure satisfactory service 
to the consumers. In illuminating plants, the most brilliant lamps 
will evidently be those placed nearest the junction between the feeds 
and distributing mains, while those of the least brilliancy will be such 
as are located midway between the two feeding-points. Experience 
has shown that a variation of 2 per cent in the voltage at any lamp 
is about as large as can be entertained compatibly with reasonably 
good service. Therefore, the value of 2 per cent of the available 
voltage, at the center of distribution, is a compulsory constant, and 
must be applied in the equations for determining the copper cross- 
section of the distributing mains. At each junction point between 
a feeder and the network of distributing mains, there flows a current 
having a maximum value sufficient to supply the territory surrounding 
the distributing center. This current must now be subdivided among 
the various distributing mains that terminate at the center of distri¬ 
bution, in proportion to the probable demands of each main. In the 


444 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


district thus to be served, the total number of lamps and their dis¬ 
tance from the center of distribution being determined from the 
map and canvass of the territory, the copper cross-section to deliver 
the required current with the specified fall of potential may be readily 
calculated by the methods already given. 

575. It should be carefully noted, however, that all calculations 
should be made for the maximum load that will ever be thrown 
upon any conductor. It has been customary to calculate a section 
of the mains for several points in the network where the heaviest 
and where the lightest loads may reasonably be expected to occur, 
and proportion the rest of the system between these extremes. Good 

engineering, however, scarcely sanctions this practice ; for while in 

* 

complicated plants full calculation is exceedingly tedious, satisfac¬ 
tory service, and economy in first cost, always warrant the most care¬ 
ful investigation and calculation of the design of the conducting 
system. If the junction points between the feeds and network are 
placed too far apart, the equations will indicate an excessive copper 
cross-section for the distributing mains, in order to prevent too 
great a fall of potential. Such a result points to the advisability of 
introducing a greater number of feeders, in order to reduce the 
copper cross-section to a minimum. Evidently a relation between 
the copper to be placed in the feeders and in the mains may be 
written, which, when differentiated and equated to zero, will give the 
minimum copper volume to be employed in the entire plant. 

576. Calculation of Feeders. — As the feeders operate as sim¬ 
ple conductors of definite length and carrying a definite maximum 
current, the calculation of the appropriate section by Ohm’s for¬ 
mula, taking into consideration the lines of economy indicated by 
Lord Kelvin, becomes exceedingly simple. The only constants 
requiring careful determination are those of the allowable fall of 
potential in the feeds, the maximum and mean currents, and time 
of operation. As no customers are connected with the feeders, 
service limitations have no bearing in the calculations for this part 
of the conducting system. Here, on the contrary, the rules of 
economy and safety become of paramount importance. It is first 
advisable to determine the maximum current to which each feed 
will be subjected, and then to ascertain the requisite cross-section 
required by heating limit to carry this current. For this purpose, 



PA PA LLEL D/S TRIE UT/ON. 


445 


formulae for current density, given in the preceding chapter, are 
available. Particular care, however, must be taken in the case of 
conduit or concentric conductors, to allow an ample margin of 
safety. Having determined the minimum cross-section for the 
maximum current, it is advisable to apply Lord Kelvin’s laws, as 
indicated in the section for “ Minimum Cost of Plant,” and “ Mini¬ 
mum Cost of Operation and Maintenance,” to determine whether 
the cross-section already found is that indicated by the dictates of 
economy. All of the necessary constants may be readily valued, 
excepting the quantities I and T, indicating the mean current and 
time of operation of the plant. These demand careful study, and 
can only be estimated by considerable experience in similar plants, 
operating under equivalent conditions to the one under considera¬ 
tion. In series plants, the determination of T and I presents no 
difficulty ; for I (the current) is a constant, and T is the total annual 
hours of operation. With parallel plants, however, the current is 
constantly varying, and to ascertain its mean annual value (the 
quantity necessary to consider) requires special investigation and 
precaution. 

577. The energy lost in the conducting system, by transforma¬ 
tion into heat, is proportional to the square of the current multi¬ 
plied by time during which it flows. Thus, if i, i', i ", etc., are the 
respective currents flowing for a time dt, then the energy wasted is 
proportional to — 


2 (A + i' 2 + i" 2 + etc.) dt, 


(224) 


which is a quantity which may differ considerably from the square 
of the mean current multiplied by the time of its flow. To deter¬ 
mine the current and time factors, it is advisable to procure a num¬ 
ber of load curves from stations probably similar to the one under 
design. From a careful consideration of these a fair estimate may 
be made. This value may be checked by a consideration of the 
probable number of consumers to be obtained for the plant, with the 
amount and length of time that they are likely to use a current. It 
is considered that 500 hours per year is a minimum for paying sta¬ 
tions. Greater values, 1,500 hours (4£ hours per day) for ordinary 
custom lighting, such as restaurants, stores, etc., or 3,600 hours for 
public lighting, etc., requiring all night service, are the customary 
averages. From a careful analysis of the probable demands for 



446 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


current, and a comparison with load diagrams of stations similarly 
situated, it is possible to deduce the probable load diagram of the 
plant with a reasonable degree of accuracy. Given the load dia¬ 
gram, the value of the expression, — 

2 (/ 2 + i' 2 + i"~ + etc.) dt, 

is most easily made by integrating with a planimeter the area of the 
load diagram. By this method the appropriate values for I and T 
are readily selected, and a solution of the equations in Chapter IX. 
indicates the appropriate economical section for the feeder ; a repe¬ 
tition of the process serving to determine the section for all the 
various feeder mains. Having determined the appropriate current 
density for the feeder, both with respect to the heating limit and 
dictates of economy, the fall of potential in each feed is given by the 
equation E — p/z/S. 

578. The question of the best number of feeds to be employed 
yet remains, and deserves careful consideration. The weight of 
copper is not increased by augmenting the number of feeds ; for, 
by multiplying the feeds, the weight of distributing mains may be 
decreased. The expense of installing and the cost of laying the 
feeders are, however, augmented to some extent by the number in¬ 
troduced. This, however, is largely counterbalanced by the greater 
saving in copper that can be made in the distributing mains ; for the 
increased number of feeds will render the potential throughout the 
network more constant and uniform, thereby reducing the amount 
of copper required in this part of the system. 

It is sometimes assumed that the weight of distributing mains in 
the network varies inversely as the square of the number of feeds ; 
while this ratio is probably too large, it is certainly greater than the 
first power, and, as will be shown, increasing the number of feeds 
forms one of the best methods for close regulation. The exact num¬ 
ber of feeds to be introduced in any plant is a question of judgment 
which can only be adequately determined by special consideration of 
the design of the plant and of the probable number of consumers. 
Beyond this no fixed rule can be given. 

579. Efficiency of the Conductors. — The minimum efficiency 
of the network of distributing mains is that which corresponds to 
the maximum current, and may be deduced from the calculations for 


PARALLEL DISTRIBUTION. 


447 


current density. A consensus of experience, in distributing plants 
of this nature, indicates that a permissible fall of potential of 7 per 
cent may, in the feeders, be allowed, 2 per cent in the network of 
distributing mains, and 1 per cent in the consumers’ wiring, reckoned 
upon the potential at the terminals of the generators. It may, there¬ 
fore, be assumed that about 90 per cent of the energy delivered by 
the station reaches the consumers. The mean annual efficiency may 
be considerably higher than this, for the instances in which a plant 
is being constantly worked to its full capacity are very rare. Occa¬ 
sional overloading, even to the extent of causing a loss in the feeds 
of from 15 to 18 per cent, will not seriously alter the annual effi¬ 
ciency, inasmuch as the time of such overloading is usually extremely 
short. Even under these circumstances, an annual efficiency of 95 
per cent or more may be reached by the conducting system. 

580. Methods of Regulation.—The prime condition demanded 
by good service is that the difference of potential at the terminals of 
the receivers shall remain constant. A network properly calculated 
does not cause a loss of over 2 per cent between the receivers, the 
feeds being so designed as to deliver equal pressures to all the cen¬ 
ters of distribution. The station should be so arranged that the 
potential delivered by the generators may be slightly varied to corre¬ 
spond to the demands of the service. Direct current distribution is 
usually effected by arranging a number of similar generators to 
operate in parallel, and connecting them at pleasure with the various 
feeders, to meet the varying demands of the service. The divergence 
of the current among the various feeders should take place in accord¬ 
ance with the demands of the customers ; and to this end it is neces¬ 
sary that the station should be able to control the supply in such a 
manner that it may take place substantially in accordance with the 
requirements of each circuit, so a knowledge of the actual poten¬ 
tial delivered from time to time at the centers of distribution is 
essential. 

531. For this purpose a series of fine wires called voltmeter 
wires, or pilot wires, are extended through the conduits from the 
centers of distribution back to the station along each of the feeder 
circuits. These wires, running from the centers of distribution, are 
permanently connected to the voltmeters in the station, and so give 
a constant indication of the pressure actually delivered at these 


448 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


points. If there are as many tell-tale wires and voltmeters as there 
are feeders, it becomes a very easy matter for the station attendants 
to keep a perfectly constant pressure at the centers of distribution. 
An improvement over this method, combining a greater sensitiveness 
with a clearer knowledge of the demands of the circuit, consists in 
supplying each of the feeders with an ampere meter having a double 
scale arranged to measure the current flowing in the feed, and the 
fall of potential thereby occasioned. 

582. The most common method of station control consists in 
introducing in each of the feeders an adequate, adjustable rheostat, 
either of wire or carbon, by means of which the current delivered to 
the feeder in question may, from time to time, be adjusted by the 
station attendant. It has been recently proposed to accomplish reg¬ 
ulation by giving the field magnets of the generators a differential 
winding, placed in series with the pilot wires returning from the 
centers of distribution, in such a manner that a fall of potential at 
the center of distribution will be followed by an increase of current 
through the field coils of the generator, and a proportional increase 
in the pressure delivered by the machine. A parallel result could 
evidently be attained by over-compounding the generators, and pass¬ 
ing the feeder current through the field coils. The difficulty with 
both of these methods lies in the necessity of so constructing the 
generators that their fields may work at a very low degree of satura¬ 
tion, in order to be sensitive to slight variations in field current, and 
in the inevitable sluggishness with which the magnetic circuits of 
large dynamos will respond to changes in the field currents, even at 
low points of saturation. 

583. A more hopeful design for automatic regulation lies in 
arranging the governor of the engine, or other prime mover, to 
respond to changes in the feeder currents, in a way to vary the 
speed of the generator. Designs of this kind are reported to be 
very successful. Regulation may also be accomplished by multiply¬ 
ing the number of feeds, with the notable advantages of a proportion¬ 
ate saving in the energy expended in the conductors, and a much 
more satisfactory service. Where regulation by a multiplication of 
feeds is undertaken, they are so arranged that they can be cut in and 
out of service, in such a manner as to vary the total resistance of the 
circuit, as nearly as may be, in proportion to the changes of load. 


PARALLEL DLSTRIPUTLON. 


449 


Then, during the hours of minimum service, only a few feeds are in 
service, and as the load increases, more and more are thrown in 
service. 

584. The Compensator. — The most ingenious, and probably 
the most successful, method of regulation consists in the employment 
of compensating dynamos, whereby such an amount of energy as is 
wasted in any feeder may be restored to the current transmitted 
from the station. To overcome the ohmic resistance of any conduc¬ 
tor requires the expenditure of a certain amount of energy. This 
expenditure of energy manifests itself in a fall of the electrical pres¬ 
sure. If, by some device, there could be added to the station output 
precisely the amount of voltage that is expended in transmitting the 
current through the feeder, the energy would always arrive at the 
center of distribution under a constant tension. Mr. W. S. Barstow 
conceived and put in practice the idea of using a small auxiliary 
dynamo, the office of which should be to add, from time to time, to 
the station’s current the required amount of voltage necessary to 
overcome the resistance of the feed. As usually arranged, a small 
dynamo is placed with its brushes in series with the feeder circuit. 
The station current, passing through the armature of the compen¬ 
sator, receives precisely the additional amount of electrical energy 
that is to be expended in transmitting the current through the feeds. 
As the increase of energy is manifested by an elevation of poten¬ 
tial, the compensating dynamo is frequently known as “ Barstow’s 
Booster.” If the compensators are made sufficiently large, that they 
may normally work along the straight portion of the characteristic, 
either the whole or any desired fraction of the main current may be 
passed through the field coils, and the device made self-regulating, 
the voltage imparted by the compensator automatically varying pre¬ 
cisely in proportion to the current output. To accomplish this 
requires a larger and more expensive dynamo ; and it is, therefore, 
frequently customary merely to pass the current through the brushes, 
depending for adjustment upon the normal regulation of a rheostat 
placed in the field circuit. In Fig. 253 is given the curve of pres¬ 
sure at the station end of a feeder in the Brooklyn Edison Station, 
as obtained from Mr. Barstow’s experiments, recorded in the Elec¬ 
trical Engineer. It is further shown that the cost of transmitting a 
current of 300 amperes over a distance of about two miles, by means 


450 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


of the compensator, averaged about -14.32 per day for the winter 
months, and 83.00 per day for the summer months. In the diagram, 
the energy added by the compensator is clearly represented, as indi¬ 
cated by the varying pressure delivered to the feeder. The constant 
in this diagram is one volt drop to every T.82 amperes. 

585. The compensator method has recently been still further 
developed by Messrs. Barstow and Mailloux in the Brooklyn Edison 
station. Here the service conditions are found to be such as to 
require the station to supply three different voltages. To operate 
sufficient independent dynamos to supply the three voltages would 
require too large a plant, and would not be conducive to good sta¬ 
tion economy. The solution of the problem is diagrammatically 
indicated in Fig. 254. 



P.M. A.M. P.M. 

Fig. 253. Curve of Feeder Pressure, Brooklyn Edison Station. 


The station is supplied with three sets of omnibus bars, one for 
high pressure, one for normal pressure, and one for low pressure. 
By appropriate switches, any feeder or set of feeders may be con¬ 
nected to any set of omnibus bars. Normally, the dynamos of the 
station represented by BB are connected to the main bus bars, 
furnishing 220 volts on a three-wire system. For the high and low 
pressure service, two sets of compensators are provided, C and C 4 
being the low pressure compensators, while C 1 and C 3 are the high 
pressure machines. The entire compensator plant is so mounted as 
to be driven from the dynamo C 2 , that, receiving power from the 
main omnibus bars, acts as a motor. When it is desired to raise the 
pressure of any feeder, the machines C 1 and C 3 , driven by C 2 , operate 
as dynamos supplying the desired additional energy. When it is 











































PARALLEL BIS TRIE UTION. 


451 





Fig. 254. Compensator for Three Voltages. 








































































































































































































































































































































452 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


desired to reduce the pressure, C and C 4 operate as motors, absorb¬ 
ing a certain amount of energy and depressing the potential. By 
this means the main generators are run at such a pressure as is 
found suitable for the majority of distributing centers, while the 
pressure to the long feeds may be re-enforced, and that in the short 
feeds diminished. The beauty in the device is the ability to change 
the pressure in any set of feeds, without interrupting the service. 
This is accomplished by a pair of auxiliary omnibus bars A 8 and A 9 , 
to which any feeder may, for the time being, be transferred. By 
means of the rheostats E and E' the pressure in the feeder after 
transference is raised or lowered to that corresponding to the high 
or low omnibus bars. The feeder is then again transferred to either 
the high or low bar, the whole operation being accomplished without 
the slightest interruption. The connections in the diagram are so 
obvious as to render further explanation unnecessary. 

585. The Compensator in Electric Railway Work. — The ap¬ 
plication of the compensator to electric railway circuits has recently 
been made by J. H. Vail, in the construction of a road from Pough¬ 
keepsie to New Hamburg. The power station is at Poughkeepsie, 
and is located centrally with reference to some ten miles of track 
extending through the streets of that town. A spur line runs due 
south connecting the towns of Wappinger Falls and New Hamburg, 
a distance of over ten miles. To avoid the excessive amount of cop¬ 
per that a line of this length would require, under the usual design of 
street railway circuits, a compensator is introduced in the station, 
that, by means of two No. 0000 feed wires, carries the necessary cur¬ 
rent to a distributing center eight miles south of the power station, 
thus supplying this section of the system, with the employment of a 
very small amount of conducting material in the overhead line. 

587. Knowing the cost of building the feeder system, the cost 
of compensator and of operation, it is a simple matter to substitute 
these values in the equations given for feeder calculations, and ascer¬ 
tain the relative economy. Under ordinary circumstances, Mr. Vail 
shows that for a plant delivering 200 amperes at 500 volts, the com¬ 
pensator system requires less initial capital investment, when the 
distance to which the current is transmitted exceeds from two and 
one-half to three miles, and that the operating expense is decreased 
when the distance exceeds one and one-half miles. 


PARALLEL DLS TRLB UTIOA r . 


453 


588. As the capital absorbed by the feeder system designed to 
maintain a constant potential varies as the square of the distance 
over which the current is delivered, while the cost of the compensa¬ 
tor varies directly as the distance, it is evident that great economy 
may be effected by this means, in long distance transmission. 

589. The compensator also adds great flexibility to the railway 
system. It is usually necessary to introduce a large amount of cop¬ 
per in the feeder system to provide for emergencies, such as excur¬ 
sions, etc., or for unusual bunching of cars at particular points. By 
the aid of the compensator, the feeder system may be designed for 
normal traffic only, and by means of a switchboard, the extra pressure 
delivered by the compensator applied to the various sections of the 
line, as occasion may from time to time require. A similar advan¬ 
tage appears in the ability to meet the load changes in a distributing 
system during the daily variation of traffic. If the circuit is calcu¬ 
lated for the hours of greatest business, the copper employed is par- 
tally idle during a greater proportion of the time ; while, if the circuit 
is arranged for the average business, it will not carry the maximum 
loading. To build the line for average work, and to put the compen¬ 
sator into service upon the system morning and evening, and on 
holidays, is an economical solution of the problem. 

590. Fall of Pressure and Necessary Section in the Feeders. — 
The pressure at the centers of distribution, where the feeder joins the 
network, being maintained constant by some form of regulator placed 
at the station in the feeder circuit under the control of the station 
attendants, the loss of pressure in the feeder is not a factor in the 
supply condition of preserving a constant potential at every consumer. 

Let S be the cross-section of one main. 

L be the length. 

I be the current. 

p be the specific resistance in any desired units, as the mil-foot, 
square-inch-mile, square-millimeter-kilometer, etc. 

V be the potential at the generator. 

v be the potential at the center of distribution. 

Then V — v is the loss in the feed, and — 


(225) 



454 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


p must be given such a value as will be cognizant of the final tem¬ 
perature to be attained by the conductor. 

591. Solving now for S' — 

s= /pZ . 

V - V 

From this expression the area of either the feeds or the distribut¬ 
ing-mains may be calculated, in so far as the variation in pressure is 
considered to be the governing condition. 

For a three-wire system, let Fig. 255 represent the feeders, Vv 
and V"v" the outer mains, while Vv' is the neutral wire. 

Let V, V', and V" represent the respective pressures at the generators. 
v, v' , and v" the pressure at the center of distribution. 

7, /', and I" the respective currents, .S’ the sectional area of the outer 
main, and S' the area of the neutral, the remaining symbols 
retaining the preceding meaning. 


v V 

V' 

v> 

V" 

V* 


Fig. 255. Diagram for Fall of Pressure in Feeders. 



Then V — V and V — V" are respectively the differences in 
pressure between the outer mains and the neutral wire at the genera¬ 
tors, and v — v' and v' — v" are the corresponding differences at the 
center of distribution. Then the drop along Vv is — 


(7- V) - (v-v') = P L^ + 


and along V" v" 


-r\ 

S' ) 

(227) 

I- I" \ 

S' / 

(228) 


592. In the best designed three-wire systems, it is customary to 
make the area of the neutral conductor equal to one-half of the area 
in either of the outer conductors. Assuming, then, that the greatest 
inequality in the balance between the two sides of a three-wire sys¬ 
tem is 2 p per cent of the maximum load, the current in the outer 
main, having the lightest load, will evidently be / (100 —/), and in 









PARALLEL D/S TRIP UTION. 


455 


the outer main with the heavy load, / (100 + p), and the current in 
the neutral wire will be p I; p being expressed in percentage. The 
value to be assigned to p will vary greatly, depending upon the care 
exercised in the balancing of the load on the two sides of the system. 
Good practice indicates the advisability of placing one-half the load 
of each consumer on each side of the mains. If this is skillfully done, 
it is rarely that the want of balance will rise above 5 or 10 per cent. 
When this arrangement is conscientiously carried out, it is impossibe 
for the load on the neutral wire to rise above 50 per cent of the entire 
load of the whole plant ; for, even in the extent of the failure of one 
of the main conductors, half of the total load on the plant would be 
thrown off, and therefore the neutral wire could, even under the most 
extraordinary circumstances, only be called upon to carry one-half of 
the total current for which the conducting system is designed. From 
experience p has been found to vary from 5 to 25 per cent for installa¬ 
tions skillfully designed. In the St. James station in London, work¬ 
ing under a maximum output of some 3,000 amperes, the variation in 
balance rarely exceeds T per cent. 

593. To determine the necessary section for the outer conductor 
of a three-wire system, let q = the relative area of the outer and 
neutral wires, then, from what precedes, — 




pLL ( 1 +pg) 


(229) 


( v _ //') _ ( z, _ */) 


From this expression it may be observed that if, in imagination, the 
resistance of the outer conductor be increased in the proportion of 
1 _|_ pq to 1, the neutral wire may be omitted from the calculation, 
and designs made as if it did not exist. 

594. The Laws of Economy in Feeder Design. — In transmis¬ 
sion parlance, the word feeder is broadly applied to any conductor in 
which the current density at any particular time is uniform at each 
point of the entire length of the conductor, no matter what the varia¬ 
tions in density may be that occur between successive time intervals. 
In other words, a feeder is such a conductor as carries for the time 







456 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


under consideration a uniform current between two fixed points. 
The current in the feed may vary from time to time, but it does not 
vary with the length of the circuit. In the simplest case of a series 
circuit, a constant current is always maintained throughout the entire 
length of each conductor, the only variable being the length of time 
during which the current acts. 

595. While it is conceivable that a series circuit might operate 
with currents of different intensity from day to day, yet such condi¬ 
tions have not been put into practice, and the time element is the 
only variable. Knowing the respective costs of the line, the station, 
and the production of energy, and the interest and depreciation 
charged on the plant, the method of ascertaining the most economical 
cross-section for the conductor has been indicated in Chapter IX. 

596. In the parallel system, conductors are found in which, by 
reason of the attachment of the receivers at different points, the cur¬ 
rent density varies from point to point along the circuit. By defini¬ 
tion, such conductors are excluded from the class “ Feeders,” being 
termed “ Distributing-Mains.” As a condition of good service, the 
pressure must be constant within very small limits, along the entire 
length of each distributing-main. With the feeders, as there are no 
customers to be supplied, the pressure may vary from point to point 
to any extent, so long as the desired voltage is given to the distrib¬ 
uting main at the point of attachment to the feeder. The current, 
however, is constant from point to point. Two diametrically opposite 
conditions prevail in these two classes of conductors. In the feeder 
the current is constant and the pressure varies. In the distributing 
main the pressure must be uniform while the current varies. With 
the feeder, then, there are no service limitations upon the variation in 
potential, and consequently the dictates of economy may be closely 
followed in the design of this part of the circuit. By multiplying the 
number of feeds, the length and size of the distributing-mains may 
be reduced to a minimum, and thus the greater proportion of the 
plant brought under the operation of economical law. 

597- Each feeder receives at one end energy from the generat¬ 
ing-station in the form of current under a predetermined pressure, 
and delivers at the other end a less amount of energy, owing to 
inevitable losses in transmission. Therefore, in every transmission 
problem the following quantities must be dealt with, any or all of 


PARALLEL DISTRIBUTION. 


457 


which may be variable ; and it is now necessary, under the circum¬ 
stances of each case, to ascertain the most economical disposition of 
the material employed in the conductor system, due consideration 
being given to the commercial aspects of both the generating and the 
receiving station. 

Let l = the pressure at the receiving end of the feeder. 
v = the pressure at the delivering end of the feeder. 

IV — the power given to the receiving end of the feeder. 
w = the power obtained at the delivering end of the feeder. 

I — the current in amperes. 

S = the cross-section of the feeder. 

L = the length of the feeder in any units. 
p = the resistance per unit of length (such as the mil-foot). 

598. I he values of L and p are always determined by the geo¬ 
graphical conditions and the selection of the conductor, and are then 
fixed for each plant. Between the other variables the following 
relations exist : — 

V - v = ID- ; W = VI ; W = vl \ 

so, if any two of the above first six variables are given, a single 
additional relation prescribed by economic law serves to fix the value 
of the remaining four. 

599. Between six variables fifteen combinations, two at a time, 
can be made. When applied to feeder design, some of these com¬ 
binations are mere repetitions of each other ; others have no practi¬ 
cable bearing, but there are eleven cases which the engineer may be 
called on to consider. These may be stated as follows : — 


Case No. 

Given. 

Required. 

Case No. 

Given. 

Required. 

1 

V, v. 

/, IV, w, S. 

7 

v, S. 

V, I, IV, w. 

2 

V, /. 

v, W, w, S. 

8 

I, S. 

V, v, IV, w. 

3 

V, w. 

v, /, W, S. 

9 

IV, w. 

V, v, I, S. 

4 

V, s. 

v, /, W, w. 

10 

IV, S. 

V, 7 ’, I, W . 

5 

v , /• 

V, IV, w, S. 

11 

w, S. 

V, V , I, IV. 

6 

v, IV. 

V, I, w, S. 





600- Each of these cases is now to be considered in detail, and 
for convenience the following notation is employed : — 

y — a + bS, equation of cost of line per unit of length. 

y' = a' -f- b'S, equation of cost of installing line per unit of length. 

L (y -f -y') or L [(a -(- bS) + (a! + £'»S)] = total cost of line. 


















458 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


i = rate of interest in per cent charged against entire cost of plant. 
di = rate of depreciation in per cent charged against cost of line. 
d c = rate of depreciation in per cent charged against cost of conduit 
or poles. 

d s = rate of depreciation in per cent charged against cost of station. 
F — number of hours that the plant operates per annum. 

K = cost in dollars of operatmg per watt or K. JV. of output. 

K r — cost in dollars of station equipment per watt or K. IV. of 
output. 

A = price in dollars received per watt or K. IV. of energy delivered. 
U' = cost of energy expended in the line. The line resistance is 
pL / S, I amperes flow for F hours, hence, pLF 2 F/ S watts 
are expended, and the cost of this is pLI 2 FK j S. The cost of 
station required to produce this energy is pLF 2 K r / S, and the 

T 7 2 Z 7 * F 

interest and depreciation on this sum is ———-(/ + d s ) ; 

hence, the total cost of the energy expended in the line, is 

V = ALL + K > <7 + ,/,)]. 

To simplify, let X = P LI 2 [ FK + K' (i + 7 S )] ; 

then, U' — X / S. Also, let co = pL [.FK -f K r (i + ^)] ; 

then, U r = w7 2 / S. 

= annual charge against the line for interest and depreciation. 
= L [(a + bS) ( i + d^) -|- {fi r -f- b'S') (i fl- d^)\ 

To simplify, let 

a = L [# -J- d \) -J- ci (i -}- 4)] and /3 — L ~b di) fl - 

b' (i + dc )]; 

then, U" = a + (3S. 

U — U' + U" = + a + /3S = total annual cost of line. 

O 

VIF = W = total power produced. 

VI \_FEC + K' (i + d s )] = total annual cost to produce IV ; also let 
Z = total annual cost to produce IV. 

To simplify, let y = \FK + K' (i + ^/ s )]; 
then, Z = V/y. 

G = gross annual expense = Z -f a -j- fiS, or V/y + a + (3S, or 
Z + U", or Vly + U". 

VI- 7 W^ - ^I(VS-IpL) 


U" 

U" 


w 


= F 


S J 


s 


To simplify, let e = VI, and 8 = I 2 pL ; 
w — F ( c- ^ 






PARALLEL DLSTRIPUTION. 


459 


Aw 


= annual income = FA 




601. Case I. — Given V and v, required I, W, zv, and S. 

As V and v are the given, the ratio of the energy received by 
the feeder to that delivered by it is fixed. It is also evident that 
the cost of the line, station, and operation (per unit of energy trans¬ 
mitted) decreases as the total output increases. Thus, there will be 
no one value of current and conductor section that will give the 
maximum economy ; but the greater the current and section, the less 
will be the expense per unit of energy distributed. The size of the 
conductor will depend upon the demand for current at the receiving- 
station ; and the larger this is, the greater the economy. 

The smallest section under the limiting values V and v, consist¬ 
ent with safety, should be employed. As a corollary, it must always 
be considered whether there is sufficient demand at the receiving- 
end to pay for the transmission of current ; for it is evident that the 
values V and v might be so limited that not enough current could be 
sold to pay for the cost of production and transportation. 


602. Case II. — Given V and I, required v, IV, zv, and S. 

Under the circumstances, VI — IV, thus fixing one of the desired 
variables. If it be assumed that there is a market for all the energy 
the circuit can deliver, it is evident that the most economical section 
is that which will make the ratio of the gross annual income to the 
gross annual expense a maximum. 


Gross income 
Gross expense 

and 


: Azv — FA VI — 
Z + aT/kS'; 


LpL\ 
s 


FA[ e ~s. 


Z T a -f- /3S 


must be a maximum ; this will occur when — 

£ _ ffi> + V/3 2 5' 2 -f- (ScSZ + /3e8a 


(230) 


603. Case III. — Given Vand zv, required v, I, W, and S. 

The pressure at the receiving-end of the feeder, and the quan¬ 
tity of energy delivered at the delivering-end, are predicated ; and 







460 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


the most economical section is that for which the cost of the energy 
expended in the line, plus interest and depreciation, is a minimum, or 
U' -j- U" must be a minimum, and also — 


VI 


PpL 

— c — = w. 
S 


By the original condition, — 

(/= + a +/IS. 


From equation (231), — 




P 9 L 


VI — w' 

substituting this value in equation (232), — 

y= «»(^-.y) +a + j8 /V . 

pL VI — w 

differentiating and equating to 0, — 

7a 


1 = 


V 


1 + 


0Z V 


(3L Y + co V *_\ 


(231) 

(232) 

(233) 

(234) 

(235) 


Having found the value of /, S is obtained by direct substitution in 
(233). 


604. Case IV. — Given V and S , required v y /, W, a)id w. 

As the pressure and section are given, it is evidently necessary 
to ascertain / to meet the economic conditions. The ratio of the 
gross income to gross expense must be a maximum ; for if it be at¬ 
tempted to make U' -f- U" a minimum, U' will become 0 when I is 
0, but U" will remain unchanged. When / is 0, there is no income, 
and there is expense without income, and the above ratio would be 0, 
and not a maximum. 


Gross income is 
Gross expense is 


and 


A 7a — FA y VI 
Z+ U 

FA VI — 


PpL_ 

S 


F 2 pL_ 

S 


Z + 6 


-// 


must be a maximum. This will occur when — 


1 = 


U" 

Vy 


V 


V 2 yS 

U"oL 


+ 1 - 



(236) 


















PARALLEL DISTRIBUTION. 


461 


Case V. — Given v and /, required V, IV, w, and S. 

605. The pressure at the delivery end of the feeder and the 
current being fixed, w = vI. It is also evident that the ratio of 
gross income to gross expense is a maximum when the cost of trans¬ 
porting and delivering the predetermined current / is a minimum. 
This occurs when U = U' + U" is a minimum, or when — 

S=^TTP- ( 237 ) 

This is the historic problem proposed by Lord Kelvin, the solu¬ 
tion of which is given in full in Chapter IX. 


606. Case VI. — Given v and IV, required V, I, w, and S. 

In this case W = ( VI), thus fixing the product of two of the 
desired variables. The section and current must be such as to make 
the ratio of the gross income to the gross expense a maximum. 

The gross income is AF v I, and the gross expense is VI y + a 
-f fiS, and 


AFvI 


must be a maximum. 

Z/ 2 


Also vl-V 

substituting, 


S 

AFv 


Vly + a + (IS 
= VI and S = 


L P I‘ 


I 


( VI) — vl ’ 


(VI) y + a + 


(3IpI- 


( VI) - vl 

To simplify, let Vly + a = ^, and fiLp (VI) = O, then — 

/ 


AFv 


* + 


Plpl- 


( VI) - vl 

must be a maximum. This will occur when — 

VI 


1 = 


and 


Z = 


O — tyv 

n 


(O — 'i' v 2 ) (O — v) V 


2 [ Vw — V K'] , 

_ “| 2 

yoi' — Oz’J . 


( 238 ) 

( 239 ) 


607. Case VII. — Given v and S , required V, /, W, and w. 

The conditions here are similar to those in Case IV.; and it is 
necessary to determine I to make the ratio of gross income to gross 
expense a maximum, under similar conditions to those in Case IV. 















462 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Gross income 
Gross expense 

and 


— Aw = FvIA. 

= vlFy +^R+ U", 


s 


FvA X 


/ 


vFyl + U 


must be a maximum. This condition will be realized when — 


»Fr + -j + — 


is a minimum, or when — 




•ft 


co 


( 240 ) 


608. Case VIII. — Given I and S, required V, v, IV, and w. 

As / and V are given, the amount of energy annually ex¬ 
pended and the charge for interest and depreciation are fixed. 
Increasing the pressure V will increase the amount of energy de¬ 
livered, and thus increase the ratio of the gross income to gross 
expense, and tending toward greater economy. 


609. Case IX. — Given W and w, required V, v, /, and S. 

Here W — w is the energy expended in the conductor; and 
as p and L are known, X can be immediately found, thus reducing 
this Case to the same condition as Case VII. 


610. Case X. — Given W and S, required V, v, /, and w. 

Under these circumstances the size of the conductor is given, 
but not the energy expended in it. As the energy expended in 
transmission varies as the square of the current, and the quantity 
of energy as the product of the current and pressure, the higher the 
pressure and the smaller the current the greater will be the energy 
delivered, and the smaller will be the cost of transporting it. Hence 
the greatest value assignable to V under the limits of safety will 
determine this quantity. The remaining unknown quantities follow 
immediately. 

611. Case XI. — Given w and S, required V, v, I, and IV 

The same reasoning and conclusions apply as in Case X. 

612. As all the economic formulae may be deduced by the rules 
for maxima and minima, the solutions beyond the deduction of the 









PARALLEL DLSTRIBUTION. 


463 


working equations have not been given. Care must be exercised in 
the selection of the proper value for I. In series circuits there is no 
difficulty or chance for error, as / can have only one constant and 
uniform value. In the parallel system I may be either the “greatest 
current ” to be transmitted, the “average current ,” or the “square root 
of the mean squares" of the varying current values. The appropriate 
methods for evaluating / will be found in succeeding paragraphs. 

613- General design for a Conducting System in Multiple 
Arc. — To skillfully plan a parallel system for the distribution of 
electrical energy, even for installations of moderate size, it is first 
essential to obtain an accurate map of the district intended to be 
covered by the central station. This map should be of sufficient 
scale to enable the premises of all of the customers to be indicated 
with a reasonable degree of accuracy, both as to the location and 
frontage along the respective streets. Supplementing such a map, 
a careful canvass of the district to be served should be made, with a 
view to ascertaining the probable customers and the nature and 
amount of service which they are likely to call for. The demands of 
urban service upon a parallel system are usually limited to supplying 
incandescent lamps and the operation of stationary motors. The 
number of incandescent lamps that will probably meet the require¬ 
ments of each consumer, may be determined by ascertaining the 
number of gas-burners, or other means of illumination, in vogue at 
the time of making the estimate, and then assuming the probable 
demands of the customer to increase from 20 to 30 per cent for in¬ 
candescent lamps, on account of the greater popularity and desi¬ 
rability of electrical illuminations. The time during which each 
customer will probably require service should also be noted as an 
important factor in determining the probable load diagram to be 
placed upon the station. A fair estimate, based upon incandescent 
installations in a number of the larger cities, indicates that about one 
sixteen-candle-power lamp may be expected for every linear yard 
of the conducting system throughout the principal streets, and about 
one lamp to two yards in the streets of less importance. Out of one 
hundred customers, 10 per cent is usually allowed for cafes and 
restaurants, 34 per cent to stores, 21 per cent to banks and mercan¬ 
tile houses, 27 per cent to theaters, and 8 per cent for residences. 
In France the figures average 28 per cent for cafes and restaurants, 


464 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


21 per cent for workshops, 271 per cent for stores, 71 per cent for 
residences and hotels, and 16 per cent for theaters and halls. 

614. Experience has also shown that it is necessary to install 
for occasional use a great many more lamps than, under any but the 
most exceptional circumstances, are ever placed in service at any 
one time. 

The following list indicates the maximum number of lamps actu¬ 
ally lighted, in comparison with the total number actually installed, 
in the lighting-plants of the following cities: — 

London ... 40 per cent. Berlin and Hamburg . 58 per cent. 

Vienna ... 52 per cent. Darmstadt .... GO per cent. 

Newcastle . . 45 per cent. Diisseldorf .... 51 per cent. 

Cologne ... 70 per cent. Hanover.55 per cent. 

615. The number of lamp-hours per lamp also forms an impor¬ 
tant consideration. From the lighting-plants in London, it is found 

* 

that in the district covered by the St. James Station, 935 lamp- 
hours per lamp per annum are obtained : from the Westminster 
station, 643 hours ; from the Metropolitan, 550 hours ; from the 
Chelsea Station, 350 hours ; and from Kensington, 354 hours. The 
St. James Station serves a district largely made up of business 
houses ; while the proportion of business to residence houses stead¬ 
ily decreases in the districts of Westminster, Metropolitan, and 
Kensington. 

616. Having completed a canvass of the district, it then becomes 
necessary to construct a load diagram for each street. An inspec¬ 
tion of the map will indicate the probable location for the various 
feeding-points. It is, in fact, hardly practical to arrange feeding- 
points at any other place than at the street intersections ; for it is 
quite essential to plan the feeder system so that each feeder may be 
adjusted to supply a maximum number of distributing-mains and 
this can be best accomplished by uniting a feeder to the several 
mains running from each street corner, extending along the streets 
radiating from such an intersection. Having made a preliminary 
determination of the feeding-points, the load diagrams for each 
street extending between two adjacent feeding-points should be 
plotted as follows : — 

617. In Fig. 256, assume AB to any convenient scale to be the 
distance from the feeding-center A to the center B. Lay off AC, 



PA RALLEL BIS TRIP UTION. 


465 


CD, DE, EF, hG, GB to same scale to represent the respective 
street frontages of the various customers. At the appropriate 
points in each house-front, place the consumer’s main, and at this 
point erect a perpendicular to AB, making each one to scale to 
represent the probable maximum circuit for each subscriber. A line 
joining the tops of the perpendiculars is the desired load-line. For 
a two-wire system, the sum of the loads on both sides of the street 
may either be plotted upon a single diagram, or two separate dia¬ 
grams made, the results of which may, on the completion of the 
calculation, be summed. 

618. For a three-wire system two diagrams are advisable, upon 
each of which half the load on each side of the street is to be 



< 60' X 160' X 60' X 60' X 120' >> 

Fig. 256. Street-Load Diagram. 

plotted. A and B, the ends of the street diagram, are the feeding- 
points from which the current enters the distributing-mains in oppo¬ 
site directions. It now becomes essential to determine the point of 
minimum pressure along the distributing-mains, the amount of drop, 
and the quantity of current which will enter the main from the 
points A and B. If the customers along B are so distributed that 
the current may, without sensible error, be supposed to be uniformly 
distributed between the two mains, the calculation of the point of 
maximum drop may be made by the equations already indicated in 
Cases I. to IV., depending upon the method of feeding and the kind 
of mains adopted. It is rare, however, that the distribution is suffi¬ 
ciently regular to allow of the assumption of a uniform distribution 















466 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


of current. For cases of irregular distribution, Messrs. Herzog and 
Stark have given an analytical method in the Electrical World of 
Aug. 23, 1890, for determining the current in all parts of a con¬ 
ducting system, no matter how complicated. The method consists 
in determining, in each mesh of the network of mains, the point of 
lowest potential, and then, in imagination, cutting the conductors 
open at this point, thus resolving the most intricate network into a 
number of elementary forms, which are comparable with Cases I. to 
IV. inclusive, and may be solved by these methods. By this means 
the system is, so to speak, differentiated into elementary parts, and 
the calculations for each element rendered comparatively simple. 
After the computations for each of the elements are completed, the 
final result may be gained by the summation of all of the partial 
calculations. While the method thus outlined gives results which 
are exhaustive in the extreme, possessing all of the elegance of 
mathematical treatment, the following plan is suggested as giving 
results which are correct within the probable accuracy of any ordi¬ 
nary canvass, and is more readily adapted to the office-work of the 
practicing engineer. 

619. An example will best elucidate the application of the 
method. In Fig. 257, let I and A be two feeding-points in a dis¬ 
tributing network supplying current to the consumers B, C, D, E, F, 
G, and H. The location of the consumers with reference to the 
points A and I, together with the currents supplied to each, must be 
ascertained, or assumed within reasonable limits. These data are 
then to be collected in a tabular form, as indicated in Table No. 53. 

Table No. 53. 


Calculations for Point of Least Pressure. 


4 

Distance 
in feet from A. 

4 

Distance 
in feet from D. 

i 

Current 
in Ampere 
per house. 

4 i 

4 ^ 

2(40 

2(40 

To B 40 

590 

5 

200 

2950 

200 


C 140 

490 

80 

11200 

39200 

11400 


D 265 

365 

30 

7950 

10950 

19350 

27800 

E 340 

290 

16 

5440 

4640 

24790 

16850 

F 415 

215 

20 

8300 

4300 

• • • 

12210 

G 490 

140 

24 

11760 

3360 

• • • 

7910 

H 565 

65 

70 

39550 

4550 

. . . 

4550 

















PARALLEL D/STRIBUTLON. 


467 


The distance of each consumer from the feeding-points A and I 
are given in the columns l x and / 2 , while the respective currents 
are in column i. In the columns headed l x i and l 2 i will be found 
the electrical moments of each consumer with respect to the feeding- 
points A and I, or the product of each consumer’s current by the 
distance of his supply lead from A and from I. The point of lowest 
pressure on the distributing-main AI is the electrical center of grav¬ 
ity of all the consumers with reference to A and I, and is to be 
obtained by summing and equating the moments. The columns 
headed and S(/ 2 z) give these sums for this example. Should 

equality between the moments on the right and left hand be found 
to occur exactly at the main of any consumer, then half of the cur- 



Fig. 257. Street Distribution. 


rent supplied to him plus all the current going to all the customers 
on the left will be derived from the left-hand feeding-point, while 
the other half of his current plus all the demand on the right hand 
will come from the right-hand feeding-point, and the greatest drop 
will be exactly at the main of this consumer. 

620. Usually, as is the case in this example, the electrical center 
of gravity lies part way between two customers ; for it is easy to see 
from the Table that D will get a portion of his supply from A, and 
the rest from I. 

Let x = number of amperes derived from A, 

and 30 — x = number of amperes desired from /; 
then 11400 + 265 * = 16850 + 365 (30 - *). 

x = 26. 


i 


























468 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


Therefore, D will get 26 amperes from A, and 4 from I. If A.repre¬ 
sent the resistance of the conductor from either feeding-point to D, 
then the total fall of pressure is — 

i (11400 + 265 X 26) N = 9145 N. 

621. To determine the necessary size to give the distributing' 
main AI, the allowable drop and want of balance must be known. 
Supposing that this example is to apply to the common three-wire 
low potential distribution, with 220 volts between the outer mains ; 
that there is a possible want of balance of 25 per cent ; and that the 
neutral wire is half the section of the outer mains. Then, remem¬ 



bering that the resistance of 1 ft. of copper conductor 1 sq. in. in 
section at 80° I 7 . (26.7° C.) is .0000086 ohm, and substituting in 
formula (229) — 

= p Lf( 1 + Pg) .0000086 X 91 45( 1 +.25 X 2 ) _ 

( V — V) - (v — v') (220 — 110 ) - (213.4 - 106.7) ' Sq ' ln ’ 

for the outer conductor, and .036 / 2 = .018 sq. in. for the neutral. 

622. Having thus determined the distributing-main between A 
and I, a repetition of the process may be employed in every street in 
the proposed distribution. By combining at each feeding-point all 
of the currents to be there delivered, the necessary feeder current 
is obtained. The feeders are now to be calculated to obtain the most 
economical action. 

























































PARALLEL DISTRIBUTION. 


469 


623. Suppose F ig. 258 to represent the territory to be supplied 
in a typical urban distributing plant, and assume it to be decided to 
employ Fowler-Warring light-armor cables laid in 10" x 10" terra¬ 
cotta conduit for the feeders. It is now required to solve equation 
(191) ; and for this purpose let the following value of the constants 
be assumed to exist : — 


K a ) 


V-, U>) 

(1) y = a + bS = 400 -f- 10000 S = cost per mile per sq. in. of con¬ 
ductor section. 


( 2 ) y 


(3) L 

(4) i 

(5) d t 

(6) d c 
(?) d s 

(8) a 

( 9 ) p 

( 10 ) p 

( 11 ) F 

(12) K 

(13) K' 

(14) / 

(15) A 
+ 75 


(<o un 

= a' + b'S = 1320 + OS' = cost per mile per duct (Jf is 0, as 
there is no variation in conduit cost with change in conductor 
section). 

= 1.75 miles (measured along the conductor, out and return). 

= 6 per cent ($.06), interest on invested capital. 

= 12 per cent ($.12), depreciation on conductor. 

= 10 per cent ($.10), depreciation on conduit. 

= 8 per cent ($.08), depreciation on station plant. 

= 1.75 [400 (.06 + .12) + 1320 (.06 + .10] = 495.60. 

= 1.75 [10000 (.06 + .12)] = 3150.00. 

= .0456 ohms, resistance of 1 mile of copper conductor of 1 square 
inch in section at 75° F. 

= 2200, hours of operation per annum. 

= 3.5 cents ($.035), cost of producing energy per K. IV. hour. 

= $75.00, cost of station per A'. IV. of output. 

= 150 amperes. 

_ pZW ^ FK i+d s )] = •- 0 - 456 --- 1 J 5 - [2200 X .035 


1000 

(.06 + .08)] 


157.5, S = y 


P 


1000 

WITtyT 

3150.00 


V.05 = .2236 sq. in. 


624. The value of a and b for the price of the light-armor ca¬ 
bles, and ci and U for the cost of the conduit, are readily deduced 
from Tables Nos. 56 and 57, in which the curves plotted are func¬ 
tions of the cost per mile and section for cable, and cost per mile and 
number of ducts for the conduit. While the curves are not perfectly 
regular, the relations, (1) and (2), are easily seen to express the 
average function of price and section and price and number of 






470 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


ducts. As there are three main feeds for every three-wire system, 
and as it is usual to lay the three distributing-mains, or at least place 
the ducts for them, where the conduit is installed, the expression for 
a'-\-b's is based on six ducts. A repetition of this process for each 
feeder of different length or of different loading will serve to com¬ 
plete all the design for the circuit to the consumer’s premises. 

625. For the inside work, the methods already given will deter¬ 
mine the requisite wire sizes for all varieties of circuits. But for the 
sake of completeness and clearness the present example will be fol¬ 
lowed to the end. Let Fig. 259 represent the house-plan having 
four circuits carrying five lamps each, and for ease in calculation 
each lamp may take one ampere; hence the conductors from the 

distribution B must be designed for 20 
amperes. Heating-limit and permissible 
drop are the governing factors in house 
wiring. 

626. As to the permissible drop, the 
best practice indicates an allowance of 
one-fourth to three-fourths of one per cent 
in the lamp circuits ; and from one to four 
per cent in the building-mains. In this 
example assume .25 per cent drop in the 
lamp circuit, and 2 per cent in the build¬ 
ing main from the street to the point B. Let the circuit distance 
from the street to B be 300 ft., that is, the total length of conductor 
employed. Turning to Table No. 26, it is seen that a 20-ampere 
circuit requires a wire .109" in diameter to be safe from overheating. 
This, from Table No. 4 is seen to be between Nos. 9 and 10 ; 
but the resistance of 300 ft. of No. 9 is .238 ohms ; and if this 
wire is used, the drop will be .792 x 300 x 20 / 1000 = 4.75 volts. 
As the allowable drop is only 2 volts, a larger wire must be used. 
To preserve the drop within the limit of 2 volts, the resistance of this 
part of circuit must be not over .1 ohm or .333 ohm per 1000 ft. 
Looking in Table No. 4, this value is found between Nos. 5 and 6. 
Probably a No. 5 would do, but No. 6 is safer. 

627. Now in the four circuits C, D, E and F, there are exhibited 
examples respectively of Cases I. to IV. inclusive, pp. 459-460. Each 
circuit must carry 5 amperes, is supposed to be 75 ft. long, and the 


street to the center of 























PARALLEL DISTRIBUTION. 


471 


drop must not exceed .25 volt. If the resistance of 1 mil-foot be 

taken at 10.61 ohms, and if 5* is the required wire section, then, from 

formula (197,) — 

v c 10.61 LI 

E =- 7 -; 

u 0 — u 

but u 0 - u' = .25, 7 = 75, and 7=5; 

hence, 7 = 10.61 X 75 X 5 / 25 = 15900 cm ; 

which, from Table No. 4, is between Nos. 8 and 9 wire. It is 
always advisable to use the size of wire larger than indicated in the 
formula. The circuits D, E, and F may be calculated in the same 
way by substituting in the formulae under Cases II., III., and IV., 
or the relative section may be at once obtained by multiplying the 
section just found by the coefficients in Table No. 51. 

then, for BZ), 15900 X 2 = 31800, or No. 5 wire, 

7*7, 15900 / 4 = 3975, or No. 14 wire, 

BF, 15900 / 2 = 7850, or No. 11 wire. 

628. For BD and BF the conductors are supposed to be 

conical, the sections given being that required at the first lamp, 
beyond which the section may taper to a point at the end of the cir¬ 
cuit. It is possible to accomplish this either by the use of a special 

standard conductor made for the particular location, or by running 

a number of separate small wires connected in parallel. In short 
circuits the saving in copper will not usually pay for the extra trouble 
involved in the conical conductors. 

629. In Table No. 54 necessary data relating to heating-limits 
may be found. Sheet 1 relates to buried conductors. The top hor¬ 
izontal line gives the loss in volts. The area of the conductors is to 
be found in the column headed “Section in Square Inches;” while 
the figures in the body of the table are ampere feet, corresponding 
to the loss in volts and sectional area. This table is calculated for 
a maximum temperature elevation in buried cables of 80° C. In 

sheet 2 will be found the data for the safe currents for aerial con- 

\ 

ductors, while on sheet 3 will be found the corresponding curves. 
In this connection, it is well to refer to the special section on the 
heating of conductors in Chapter VII. 

630. Mechanical Methods. — The preceding solutions are en¬ 
tirely algebraical. It is occasionally customary to lay out upon a 
reasonably large scale a map of the district to be served, and then 



472 THE ELECTRICAL TRANSMISSION OF ENERGY. 


»o 

o 

£ 

w 

A 

M 

< 

H 







































PARALLEL DISTRIBUTION. 


473 


to build a model network of wire of reduced gauge to correspond in 
resistance to the scale of the map ; and then, by supplying the net¬ 
work so designed with a battery current, and measuring the fall of 
potential in various spots by means of a voltmeter, to make the 
determination of the location of the central station, the size of the 

Table No. 54. 

Heating-Limits for Conductors. Sheet II. — Aerial and Paneled Conductors. 


Size of Wire 

B. & S. G. 

Section 
i.i Sq. Mils. 

Resistance in 
Ohms 

Per 1000 Ft. 

Current in 
Amp. for 
W ire in Panels. 

Current in Ampere 
for Conductors in Still Air. 

Current in Ampere 
for Aerial Conductors. 

5° 

10° 

20° 

40° 

80° 

5° 

10° 

20° 

40° 

0000 

166190 

.05012 

175 

104 

146 

204 

288 

403.8 

229.6 

331.6 

461 

636 

000 

131790 

.06320 

143.5 

89 

125 

177 

248 

345.9 

198.1 

280.6 

388.6 

536 

00 

104518 

.07969 

124 

77 

106 

152.7 

214.9 

299 

169.7 

237.9 

328.9 

453 

0 

828S7 

.1004 

103.5 

67 

93 

132 

186.8 

257 

143.8 

200.8 

280.8 

383.5 

1 

65732 

.1267 

87 

57 

84 

115.6 

160.9 

222.7 

121.8 

168.7 

236.8 

326 

2 

52128 

.1598 

73 

50 

69 

99 

140 

192.3 

102.5 

141.8 

198.4 

272 

3 

41329 

.2015 

62 

44 

60 

86 

121.6 

166.4 

86.7 

120.4 

169 

234 

4 

32784 

.2541 

51.5 

39 

52 

74 

105.75 

143.8 

73.1 

101.5 

143 

198.7 

5 

25999 

.3204 

43.5 

34 

47 

66 

92.5 

125.5 

62.6 

87 

122.5 

170 

6 

20618 

.4040 

36.5 

29 

42 

58 

81 

109.6 

53.5 

74.6 

104.8 

145 

7 

16351 

.5094 

30.75 

25 

37 

50.6 

71 

95.5 

45.6 

63.7 

89.2 

123 

8 

12967 

.6424 

25.75 

22 

32 

44.4 

63 .<3 

83.5 

39.3 

55 

77 

106 

9 

10283 

.8100 

21.75 

19 

28 

37.5 

57.1 

72.6 

33.6 

47.5 

66 

90.4 

10 

8155 

1.021 

18 

17 

24.3 

33.7 

50.5 

62.8 

28.7 

41 

56.4 

77 

11 

6467 

1.253 

15 

15 

22 

29.6 

45 

55.7 

24.8 

35.4 

48.5 

66 

12 

5129 

1.624 

13 

13 

19.5 

26 

39.5 

49 

21.8 

30.8 

42 

57 

13 

4067 

2.048 

11 

11 

17 

22.9 

34.5 

42.5 

19 

27 

37 

49.6 

14 

3225 

2.582 

9 

9.5 

15 

20 

30.1 

37.5 

16.5 

23.9 

32.2 

42.6 

15 

2558 

3.256 

7 

8 

13.5 

17.5 

26 

32.7 

14.2 

20.2 

27.5 

36.1 

16 

2029 

4.106 

6 

rr 

i 

12 

15 

22 

28 

12 

17 

23 

30 

17 

1609 

5.178 

5.25 



. • 


• • 

• • 

• -- 

• • 

• • 

18 

1276 

6.529 

4.6 



• • 


• • 

• • 

• • 

• • 

• • 

19 

1012 

8.233 

4 



• • 


• • 

• • 

• • 

• • 

• • 

20 

802.3 

10.38 

3.5 





• • 

• • 


• • 

• • 

21 

636.3 

13.09 

3 



• • 


• • 

• • 

• • 

• • 

• • 

22 

504.6 

16.51 

2.5 



• • 


• • 

• • 

• • 

• • 

• • 

23 

400.2 

20.82 

2 



• • 


• • 

• • 

• • 

• • 

• • 

24 

317.3 

26.25 

1.6 



• • 


• • 

• • 

• • 

• • 

• * 

25 

251.7 

33.10 

1.4 



• * 


• • 

1 






r^eds and distributing-mains, and the fall of pressure at various 
points, entirely in an experimental manner. For very large plants, 
and those presenting peculiar complexities, a practical method of this 
kind has certain advantages, especially as the model may afterward 
be preserved as a facsimile of the conducting system ; and may, from 
time to time in the future, be used to afford means of solving prob- 
























































474 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


o' 

£ 

w 

C 

H 



S3y3dlAlV 


































PARALLEL DISTRIBUTION. 


475 


lems relative to the addition or extensions to the conducting system, 
or the introduction of new customers. Such a method is, however, 
usually considerably slower and more expensive than the analytical 
one ; and erroneous deductions, due to imperfections in the scale 
ratios, are likely to be serious. To determine the point of greatest 
drop, a method embracing a mechanical application of the principle 
of moments is, however, rapidly and accurately available. 

631. Suppose a scale-beam to be arranged as shown in Fig. 260, 
with the supporting pivot at the center, the length of the scale-beam 
L and L' at either side of the pivot being so arranged as to corre¬ 
spond, on any desired scale, to the length of the street between the 



A B C D E 


distributing-centers under consideration. Between the points a and 
/, on the left-hand side of the pivot, arrange scale-paps at distances 
to correspond to the consumers’ frontage along the street. Arrange 
a corresponding set of scale-pans upon the right-hand side of the 
pivot in the same order as those indicated in the left-hand side, and 
balance the beam. In each of the scale-pans on the left-hand side, 
place weights corresponding to the amounts of current required by 
the respective customers. Now remove the weights from a, and 
place them in the corresponding pan on the right hand of the sup¬ 
porting pivot. Continue this operation until the scale-beam again 
balances about the center pivot. Suppose, when equilibrium is ob¬ 
tained, the weights in the scale-pans A, C, and D have been removed 
from the left-hand side of the lever, and have been placed upon the 
right-hand side, the interpretation of this result. means that the 

































-_76 THE ELECTRICAL TRANSMISSION OF ENERGY. 

point of lowest pressure is located at a distance from a equal 
to ae. 

632. It sometimes occurs that equilibrium can be obtained only 
by dividing the weight in one of the scale-pans. Thus, for example, 
supposing all of the weights in A, C, and D to be removed to the 
right-hand side of the lever, and one-half of the weight in E. It is 
evident, under these circumstances, that the point of lowest potential 
is at the point e, and that one-half of the current supplied to e comes 
from a and one-half from f 

633. Station Loads. — The behavior of a central station under 
the load thrown upon it, and a study of the variation in the loading 
due to business emergencies, form one of the most interesting and 
attractive of investigations for the electrical engineer. This exami- 
nation is chiefly attractive to the central station designer ; the results 
of the investigation of station-loading being valuable in the solution 
of transmission problems, only as they afford means of determining 
the probable loads and variation in loading to which the circuit will 
be submitted. In the elucidation of this part of the problem, experi¬ 
ence is the only guide. As an exponent of the loading to which the 
central stations in urban districts may reasonably expect to be sub¬ 
mitted, the curves given in diagrams Nos. 1 to 17 inclusive, Fig. 261, 
are presented. The curves numbered from 1 to 12 inclusive are the 
average monthly curves obtained from the operation of St. James 
Station in London ; they are exhibited by the London Elcctriciaii as 
sample curves, giving a fair indication of the monthly output of the 
St. James Station during the period of a year. In each curve the 
horizontal axis to a scale of sixteen hours to an inch represents 
the hours of the day, while the vertical axis represents 1,600 am¬ 
peres to the inch. The heavy line in each of the diagrams indicates 
the current output for each hour of the day in one main conductor, 
while the dotted line gives the current flowing through the other 
wire, requiring an algebraical summation to give the total station 
output ; the departure of the dotted line from the full line fairly 
represents the amount of unbalance to which the plant was sub¬ 
jected. An examination of all of the curves reveals a close fam¬ 
ily resemblance existing between them. In every instance the 
quantity of current slowly increases from 5 a.m. to about 3 p.m. 
From this time until from 5 to 9 p.m. the current rises sharply, 


amperes amperes Amperes amperes 


PARALLEL DISTRIBUTION. 


477 


Fig. 261. Curves of Station Output 



HOURS 


No. 1. Jan. 12, 4,514 Units. 



No. 3. March 9, 3,672 Units. 




HOURS 

No. 4. April 13, 3,229 Units. 



HOURS 

No. 5. May 18, 2,149 Units. 


1800 

1600 

1400 

W 1200 
ui 

a. looo 

id 

n 800 
600 
400 
200 


5 

< 




































»\ 

11 













1 

\ 














\ \ 











) 


\ 1 
\\ 



















i 

























7 9 11 1 


3 5 7 9 11 1 

HOURS 


3 5 7 


No. 6. June 8, 2,529 Units. 



HOURS 



HOURS 


, Aug. 10, 1,973 Units. 


No. 7. 


July 20, 2,082 Units. 


NO. 8 









































































































































































































AMPERES AMPERES AMPERES 


478 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


Fig. 261. Curves of Station Output. ( Continued.) 



No. 9. Sept. 7. 1,980 Units. 



*5 79 11 13579 11 1357 
HOURS 

No. 11. Nov. 23, 5,345 Units. 



HOURS 



01 —— — --— -— 

5 79 11 13579 11 135^ 
HOURS 

No. 10. Oct. 26, 4,267 Units. 



579 11 13579 11 1357 
Hours 

No. 12. Dec. 14, 4,822 Units. 



Ja. Fb.Ma.Ap.My.Jn.Jy. Au.Sp.Oc.Nv.Dc. 


No. 13. Heavy Fog, 7,942 Units. 


No. 14. Curve of Annual Output. 
















































































































































































PARALLEL DISTRIBUTION. 


479 


Fig. 261. Curves of Station Output ( Continued.) 


Noon Midnight Noon 


































































































































































































480 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


usually attaining a maximum value between the hours 7 and 9, 
the variation in the maximum having its origin in the varying 
length of the days from month to month. The total Board of 
Trade units delivered by the station is indicated upon each dia¬ 
gram. From January to August the station output regularly de¬ 
creases, attaining a minimum in August. The minimum current 
at this time is not only due to the greater length of days, but is 
also owing to vacation absence during the month of August of the 
greater part of the business population. If the current curve fol¬ 
lowed strictly the relation between the lengths of day and night, 
the minimum would evidently occur in the early part of July, in¬ 
stead of August. In September and October the current output 
increases toward a maximum more rapidly than the decrease oc¬ 
curred in the earlier part of the season, indicating a resumption 
of business in September. The curves for November and Decem¬ 
ber are very nearly alike in output, showing that the maximum 
demand is thrown upon the station a little earlier than the occur¬ 
rence in the shortest days of the year ; for it is a noticeable fact 
that, although the actual length of the day is a minimum in De¬ 
cember, the amount of cloudy weather which occurs in the latter 
part of October and November makes a greater proportional de¬ 
mand for light in these two months. Diagram No. 13 is exhibited, 
showing the remarkable fluctuations and extraordinary demand on 
the station due to exceedingly stormy and foggy weather. Here 
the ..maximum current output occurred between the hours of 3 and 5 
in the afternoon, instead of between 5 and 7, as in the normal De¬ 
cember curve; the output in this case being nearly 8,000 units 
against the normal December output of 4,800, nearly doubling the 
demands upon the station. 

In diagram No. 14 a summary of the year’s work is given by 
plotting the output of each month. Here the vertical axis indicates 
the station output at the rate of 8,000 units per inch, while the hori¬ 
zontal axis is at a scale of 8 months to the inch. 

634. In diagrams Nos. 15, 16, and 17 are represented the curves 
obtained from the Cincinnati Edison Station, the Boston Edison 
Station, and the Brooklyn Edison Station. All of these bear a strik¬ 
ing similarity to the London curves, exhibiting, however, some local 
peculiarities. In the diagrams from Cincinnati and Boston, the 


PARALLEL DLSTRLBUTION. 


481 


theater load brings a noticeable elevation into the curve at eight 
o clock in the evening. In Brooklyn a similar rise of current may 
also be noted, but this is much smaller in comparison than in the 
previously mentioned cities. This is owing to the greater propor¬ 
tion of residence population in the district served by the Brooklyn 
Station. 

635. A study of station load curves affords to the designer the 
best indication of the amount of load thrown on the conductor sys¬ 
tem, from which a deduction of the amount of current and the time 
of flow can be most accurately made, for application in the economi¬ 
cal formulae. To determine the mean annual current most accu¬ 
rately, as great a number of diagrams as possible should be procured 
from the station under consideration, or from one as nearly similar 
to it as practicable. If it is possible to 
obtain the daily load curve for a year, an 
accurate determination of the constants 
may be made. Professor Patterson of 
Michigan has indicated an extremely in¬ 
genious method for the solution of this 
problem, which may be best illustrated 
by applying his process to the deter¬ 
mination of the amount of mean output 
of the St. James Station. Assuming the 
curve of annual output as indicated in 
diagram No. 14, draw a circle, Fig. 262, 
having a radius equal to the greatest ordinate of this curve, and 
subdivide the circle into twelve equal parts, by drawing radii to 
the circumference at the points Ja, Fb, Ma, Ap, My, Jn, Jy, Au, 
Sp, Oc, Nv, and Dc, each corresponding to a monthly ordinate in 
No. 14. Upon each of the radii lay off, from the center of the circle 
outward, a distance equal to the ordinates of the curve in diagram 
No. 14. By connecting all of these points an area will be obtained, 
which is indicated by the shading in Fig. 262. Find the area of this 
shaded curve by means of a planimeter, and then find the radius of a 
circle corresponding in area to the area of the shaded portion. The 
radius of this circle will, to the scale selected for the original circle, 
and corresponding to the monthly load diagram, be the amount of 
the mean annual output; for, evidently, each elementary area of the 


Ap. 





Fig. 262. 

Diagram to Determine Mean Annual 
Current from Station Load Curves. 





482 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


shaded figure is proportional to the square of the radius vector. In 
the illustration given, the circle corresponding in area to the shaded 
figure is given by a dotted line, the radius of which is .42". Diagram 
14, Fig. 261, is 8,000 units per inch, consequently the mean annual 
output of the St. James Station would be 8,000 x .42 = 3,360 units. 

636. Algebraically the same result may be arrived at by finding 
from the load diagrams the maximum current output, and then ascer¬ 
taining the relative lengths of time that the plant operates under 
different fractions of maximum load, say at intervals of 5 per cent, 
from 5 per cent to 100 per cent. Then, by multiplying the number 
of hours by the square of the percentage time operation, and extract¬ 
ing the square root of the sum, the square root of the mean square 
of the annual current is obtained. 

637. Arc-Lamps on Constant Potential Circuits. — For every 
purpose excepting that of arc-lighting, the constant potential circuit, 
from its greater economy, lower pressures, and greater flexibility, has 
received a greater development. Many attempts have been made to 
operate arc-lamps upon constant potential circuits ; but the variation 
in the voltage of the circuit, together with the necessity of the intro¬ 
duction of large, wasteful resistances, has prevented, until recently, 
the wide adoption of this practice. Successful lamps now, however, 
are constructed to operate upon constant potential circuits, and the 
number of these installations is now very rapidly increasing. Lamps 
are arranged across the constant potential mains of a 110 volt circuit, 
by placing either two or three lamps in series. In the case of two 
lamps in series, each lamp would operate at from 40 to 45 volts, 
thus consuming from 80 to 90 volts out of the possible 110 volts. 
Under these circumstances, from 20 to 30 volts would be lost in the 
necessary wasteful resistance, to be inserted in series with the lamps. 
In many cases, this amount of waste energy is not a serious factor, 
in a consideration of the other advantages to be derived from the 
constant potential circuits. The same lamps, however, may be ad¬ 
justed to run on a 35 volt arc, by means of which three lamps may 
be placed in series, thus taking 105 volts, and necessitating only a 
loss of 5 volts in extra resistance. In a similar manner, six lamps 
may be placed in series across the outer mains of a three-wire cir¬ 
cuit. The lamps, also, may be adjusted to take from 3 to 20 am¬ 
peres, by this means permitting a great variation in the amount of 
candle-power delivered to the consumer. 


PARALLEL DISTRIBUTION. 


483 


638. Electrical Railway Wiring. — So far the distribution of 
electrical energy under the parallel system has been considered only 
for the case in which the receivers and the station were placed at 
constant and fixed distances from each other. A very important 
application of the system has arisen in the construction of electrical 
railways, in which the receivers are constantly varying the distance 
between themselves and the station. The electrical railway problem 
is also further complicated by the fact that the load thrown upon 
the station is rapidly varying throughout very wide limits. Take the 
case of a small road operating a single car. It is evident that at 
each stop and start of the car the entire station load will be thrown 
off and on, thus causing the station output to vary from zero to a 



Fig. 263. Station Diagram, Nauesinh Mountain Railway. 


maximum many times an hour. As more and more cars are oper¬ 
ated, the station load becomes more nearly constant ; but even with 
roads of the largest capacity, the variation in the station load is large 
in comparison with that thrown upon ordinary lighting plants. 

In Fig. 263 is shown the variation of station load upon a road 
carrying four cars. The curves here given are by Messrs. Herring & 
Aldrich, from a test made upon the Navesink Mountain Road. The 
time during which the measurements are taken covers a period of 
fifty minutes ; and during this short interval of time, with four cars 
in operation, the load on the station has rapidly vaiied from zeio 
nearly to 300 amperes. 

639. In Fig. 264 the load diagram of the Minneapolis Street 
Railway is shown. Here 142 motors were in operation, requiring an 




















































484 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


average current of 1,1 G8 amperes. Even with this large number of 
cars in service, the station load varied from 600 to nearly 1,800 
amperes within three hours. Many variations of 400 to 500 amperes 



Fig. 264. 


occurred within a few minutes of each other. It is plain, from an 
inspection of these diagrams, that the demands on the conducting 
system of an electrical street railway are exceptionally severe, and 
great precautions must be taken to proportion the wiring in such a 



Fig. 265. Load Diagram, Philadelphia Traction Company. 


manner as to readily respond to the severest calls that may be made 
upon it. 

640. In Fig. 265 the load diagram from one of the stations of 
the Philadelphia Traction Company is given as an example from a 
large and heavily loaded road. Here the variation between the night 
and day load is striking, but the effect of a large number of cars to 
smooth out and even the general line is still more noticeable. From 





































































































PA RALLEL DISTRIE UTIOA r . 


485 


these examples the designer can gather a close approximation to the 
probable load line of the plant under consideration. 

641. The electrical railway system should be constructed upon 
the feeder and main system ; but it is impossible to secure the advan¬ 
tage of connecting the distributing-mains and feeders together, form¬ 
ing a network, for the reason that, in order to avoid interruptions of 
traffic upon the entire road, it is essential that the trolley wire shall 
be split into a great number of sections, each one of which is inde¬ 
pendent of any and all other sections. This precaution is necessary 
in order to avoid shutting down the whole line in case of a short cir¬ 
cuit at any point. Should the wiring be a continuous network, it is 
evident that the grounding of any portion will throw the whole road 
out of commission ; while, if the trolley wire be subdivided into numer¬ 
ous separately insulated sections, the accidental disarrangement of 
any one will in no wise interfere with the traffic of the road, excepting 
in the section injured. For this reason, it is customary to subdivide 
the trolley wire into a number of parts, each one of which is entirely 
insulated, and provided with a separate circuit to the station. Such 
a form of wiring is evidently the feeder and main system in the sim¬ 
plest form. Each section of the trolley wire forms a distributing- 
main that is connected to the station by means of its appropriate and 
special conductor. To determine the load diagram of an electrical 
railway, which is an essential consideration in the calculation of a 
conducting system, it is necessary to ascertain the number of cars 
which will at any one time be concentrated on any section of trolley 
wire, and the maximum amount of current to be taken by each car. 
To this end, it is essential to secure a plan and profile of the road, 
showing where the grades and curves occur, and where the travel is 
likely to be a maximum, requiring the greatest number of stops and 
starts, also where the cars will be most heavily loaded. Of all the 
factors entering into the problem of railway wiring, the live load in 
the car plays the part of least importance. The difference in the 
current required by an empty car and a fully loaded car is but a small 
proportion of the current required to start a car, or move it upon 
curves and grades. For an ordinary car carrying two fifteen to 
twenty-five horse-power motors, an average running current of from 
fifteen to thirty amperes is required. To start the same car upon 
curves or grades will cause the starting current to rise to fifty or 


486 


TIIE ELECTRICAL TRANSMLSSLON OF ENERGY. 


even one hundred amperes for a few moments. The severest stress 
to which the conducting system of an electrical railway circuit can 
be subjected occurs in the case of a blockade, when a large number 
of heavily loaded cars may be expected to start almost simultane¬ 
ously. It is for cases of this kind that the wiring of the road should 
be most especially planned, for nothing is so detrimental to street¬ 
car motors as to subject them to the requirements of starting under 
an excessive fall of potential. Such a stress as this almost invariably 
injures the insulation of the armature, causing the motor to sooner 
or later burn out. It is, therefore, advisable to prepare the load dia¬ 
gram of each section of the trolley wire with the maximum possible 
current in view, bearing in mind particularly, that experience has 
shown that traffic on electrical railway lines immediately increases 
upon the introduction of the electrical system, usually indicating it 
advisable to double or triple the load which is, or has been, carried 
by other forms of traction on the same line. Having obtained the 
load diagram for each section of the trolley wire, the calculation of 
the fall of potential in a particular section of trolley wire is an ex¬ 
ceedingly simple matter. The calculation of feeders for each section 
of wire may be made according to the formulae already given. It is 
usually advisable to extend the feeders to the center of each trolley 
wire section, and then to branch the feeders longitudinally along the 
trolley wire for such a distance as will enable the feeds to supply the 
required current under the given fall of potential clear to both ends 
of the section. While railway motors are sensitive to changes in 
the potential, they will bear a much greater variation than incandes¬ 
cent lamps, so it is customary to design the conducting system of an 
electrical road to work under a difference of potential for an average 
maximum current of from 50 to 75 volts on a 500-volt circuit. The 
mean annual current for a road is so difficult to predict, previous to 
the operation of the line, that it is exceedingly hard to apply the 
formulas for maximum economy. Experience has also shown that in 
most cases the most economical current density requires the con¬ 
ducting system to vary over too great a difference of potential to 
enable the motors to safely and successfully operate. The condi¬ 
tions, therefore, which usually limit electric railway wiring are those 
of the maximum allowable fall of pressure, which should never exceed 
10 to 12 per cent of the available voltage at the station. To com- 


PARALLEL DLSTRIBUTLON. 


487 


pensate for the drop in the line, it is advisable to over-compound the 
generators at the station, that, with an increased demand upon the 
conducting systems, the voltage of the generators shall rise in pro¬ 
portion to the demand upon the line, thus enabling a very notable 
saving in the cost of the conducting system to be made. 

642. Three-Wire Railway System. — A recent novel and suc¬ 
cessful experiment in three-wire distribution has been put into opera¬ 
tion by the electric railway companies in Portland, Oregon, and in 
Bangor, Maine, for supplying energy to the street railway. The 
station and railway lines are planned on three-wire system, the gen¬ 
erators running at 1,000 volts; the trolley wires throughout the 
double track being respectively the positive and negative leads, 
while the ground return assumes the function of the neutral wire. 
The feeder system is designed to operate with the trolley wire, and 
is split into two halves, corresponding in sign to the trolley wire. 
Accidental grounds on the line only interrupt service in the section 
in which the defect occurs. By careful scheduling, the car-load is 
so proportioned that excessive unbalancing of the system does not 
occur, and for more than a year the plan has been in successful 
operation. 

If the topographical conditions of the country are such, and the 
arrangement of the schedule will permit of quite an accurate balance 
of the load upon the two sides of a three-wire system when applied 
to an electrical railway circuit, there is no reason why this method 
should not be successfully adopted ; and experience in the above- 
named cities demonstrates that it can be done. As the only reason 
for adopting the three-wire system in an electrical railway is economy 
in conducting material, and as the endeavor to continually maintain 
a proper balance between the two sides of the system is rarely 
uniformly successful, it would hardly seem as if the game were 
worth the candle, under ordinary circumstances. Usually economy 
in copper section could be better attained when the power station is 
located at a distance from the electrical center of gravity of the 
road, by adopting some form of motor transformer to permit of the 
station being operated at a high potential, while the line runs under 
the ordinary 500 volts. 


488 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


CHAPTER XI. 

MISCELLANEOUS METHODS. 

MOTOR TRANSFORMERS, ACCUMULATORS, TRANSFORMERS, THE POLY¬ 
PHASE SYSTEM, AND LONG DISTANCE TRANSMISSION. 

643. In the description of multiple-wire systems, it has been 
shown that economy in distribution can be effected by raising the 
potential of the generator station, and decreasing the current through 
the conducting system ; but, at least in lighting-circuits, a practical 
limit is soon reached to the possible elevation of potential, by the 
limited resistance of incandescent lamps, and the independence of 
the various customers is seriously interfered with in the attempt to 
run several lamps in series, in order to render elevated potential 
available. Many attempts have been made to render feasible distri¬ 
bution at high voltages, in order to cover large areas without too 
serious loss in the conducting system, and without too great an 
expenditure of capital for the conductors, by means of auxiliary 
pieces of apparatus, whereby a high voltage and small current 
supplied by the station could be transformed and changed into a 
lower voltage and greater current for the consumer. 

Devices of this kind have been more or less successful, and 
already have attained so wide an introduction in distributing systems 
that, while the consideration of the various appliances used in this 
connection more strictly belongs to a discussion of station machinery, 
yet no treatise upon electrical distribution would be complete with¬ 
out, at least, a limited reference to the various systems that have 
thus been inaugurated. 

644. Motor Transformers. — The modern motor transformer is 
a dynamo machine, the armature of which contains two circuits and 
two commutators. These commutators are usually arranged upon 
opposite ends of the shaft extending through the armature, so that 
essentially the machine may be said to be two dynamo machines, 
excited by the same field magnets. The high potential line from 
the station is brought to the brushes of one of the commutators, 



MISCELLANEOUS ME TI/ODS. 


489 


to which the fine wire windings of the armature are attached, and 
the machine acts as a motor, the armature rotating rapidly between 
the poles of the fields. The field magnets are in a similar manner 
excited by the line current. Now, it is evident that the other set of 
windings of the armature, being rotated in a powerful magnet field, 
will behave as a dynamo generating a current, that, flowing out 
through the remaining commutator, may be used in precisely the 
same manner as a current from any other source of electrical energy. 
From a study of the principles governing dynamo electric machinery, 
it is known that the voltage produced by a dynamo acting as a 
generator, or absorbed by one acting as a motor, is proportional to 
the rate at which the armature conductors cut the magnetic lines of 
the field. In the case of the motor generator, inasmuch as the 
armature runs in a constant field, the voltages on the two commu¬ 
tators will evidently be proportional to the number of turns in the 
respective halves of the armature. Thus, by making the windings 
of that portion of the armatures connected to the line of fine wire 
and a great number of turns, while those on the generator side are 
of coarse wire with a small number of turns, it is perfectly feasible 
to transform the high potential and small current supplied by the 
station line to a low potential and large current for consumers’ use. 
So, in cases where distribution is required over a very large area, it 
is possible to design the main source of supply to distribute a small 
current of a few amperes at a high potential (say several thousand 
volts), running the primary conducting system to a number of sub¬ 
stations, which approximately take the place of centers of distribu¬ 
tion in the feeder and main system. 

645. At each of the subordinate stations, by means of a motor 
transformer, the small current and high potential of the original 
supply is changed to a large current at low voltage, giving a safe and 
practical supply for all consumers. Such an arrangement leads to 
marked economy in the primary conducting system, especially if the 
geographical circumstances are such as to necessitate the expansion 
of the system over a large territory, and also renders all of the 
customers entirely independent of each other. The various motor 
transformers may either be operated in series or in parallel ; and, 
furthermore, additional advantage may be obtained by arranging 
either the primary or secondary system, or both, to operate upon the 
multiple-wire system. 


490 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


646. Installations of this kind have already reached considera¬ 
ble development, especially in Europe, where by their aid widely 
extended distribution is made a commercial success. Little or no 
difficulty is experienced with the motor transformers, as, by careful 
proportioning, these machines may be made exceedingly permanent 
and durable, requiring for annual maintenance only the renewal of 
the commutators and the brushes ; and when suitably calculated for 
the loads placed upon them, they can be made exceedingly economi¬ 
cal, having an efficiency of over ninety per cent at full load. As, 
however, they are dynamic machines, a certain amount of supervision 
is essential; and, therefore, usually an attendant is constantly re¬ 
quired at each of the sub-stations during such times of the day as 
the motor dynamos are in operation. The expense of maintenance 



and lack of efficiency of the motor generators are comparatively 
small items, being usually much less than the cost of interest, depre¬ 
ciation, and loss of energy in the ordinary conducting systems. The 
cost of attendants, however, is quite a serious item, and has so far 
limited to a notable extent the expansion of this system. The 
system just outlined for the employment of motor transformers is 
one that has received, perhaps, the largest sanction by experience. 
There are, however, many special methods, of which the following 
are perhaps the most important. 

647. Compensators. — The use of motor generators for com¬ 
pensator has already been alluded to. The design of a compen¬ 
sator plant will be more clearly understood by reference to Figs. 266 
and 267. 

The simplest case is the employment of a compensator upon the 
three-wire system, the outline of the connections being shown in 






M/SCELLANEOUS ME THODS. 


491 


I ig. 266. A is the generating-station, B and C being the two 
compensators. These compensators are two dyamos, shunt wound, 
the fields being placed across the outer mains, as shown at F and G. 
The armatures of the two compensators are wound upon the same 
shaft, in ordei to rotate exactly in unison. When the two outer 



conductors of the line are equally loaded, a very small current flows 
through the compensators, simply sufficient to turn the armatures, 
overcoming the frictional resistance. As soon as the system be¬ 
comes unbalanced, the armature connected with the main carrying 
the least current becomes a motor, while the other armature plays 


^ 4 



Fig. 268. Diagram of Currents in Five - Wire Compensator. 


the part of a dynamo, the balance of the system being restored ; for 
one of the compensators, acting as a motor, drives the other arma¬ 
ture as a generator, furnishing the excess current required upon the 
overloaded main. 

648. The calculations for the amount of current required 
in the various compensators may be made by the application of 
Kirchhoff’s laws. Fig. 26T gives an illustration of the compensator 































492 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


method, as applied to a five-wire system, and will form a sample to 
elucidate the application of the calculations. 

Let X be the current from the station ; 

«, /, q the currents in the different receivers; 
e the voltage of the receivers ; and 
E — 4 e, the voltage of the station. 

649. Let A, B, C, D, and E, and A', B', C', D', and E' be 
the respective mains, with the compensators located between A'B', 
B'C', and D'E'. By Kirchhoff’s laws, the values of the currents in 
the intermediate wires may be readily found, as indicated in the 
illustration. 

If X is the current supplied by the station, and x, y, z, and t the 
currents in the armatures of the compensators, the following equa¬ 


tions are readily deduced : — 

X + x — m = 0. (241) 

y -j - m — n — x — 0. (242) 

z + n — p — y = 0. (243) 

q -t -X = 0. (244) 

From which m — x — n — y = p — z = q — t = X. 


650. Moreover, if it is assumed that the compensators have an 
equal output, whether acting either as generators or motors, and 
neglecting the small amount of energy expended to overcome their 
ohmic resistances, and assuming e to be the electro-motive force 
required for the lamps, the following equation obtains : — 

4 eX = e (m + n + / + q) ; (245) 

From which m + n +p + q / 4. (246) 

651. Solving, the various values for the currents in the compen¬ 
sators and in the separate wires, as indicated on Fig. 268, are ob¬ 
tained. As all of the compensators are shunt wound machines, 
having their fields excited between the outer conductors, they always 
revolve in the same direction, no matter whether acting as generators 
or motors ; and, under the present state of perfection in dynamo con¬ 
struction, they require an exceedingly small amount of attention. 
The independence of the system is further preserved by the ability 
to insert compensators at any number of points across the primary 
mains. This method renders it feasible to operate a station by an 



MISC EL L A NE O US ME THODS. 


493 


available water-power, situated at some distance from the center of 
gravity of the consumers, delivering the energy thus obtained at a 
high potential through a small pair of conductors, and placing the 
compensators in parallel across the mains at the various centers of 
distribution. To determine the size of the compensators, it is ne¬ 
cessary to establish the greatest possible difference in loading be¬ 
tween the outer conductors and any of the intermediate ones, and 
proportion the compensator to deliver the current thus indicated. 
By designing the system according to the observance of precautions 
indicated for the multiple-wire systems, so that the load of the vari¬ 
ous consumers shall be equally subdivided among the intermediate 
conductors, it is practical to reduce the probable lack of balance to 
a small percentage, thereby reducing in a corresponding proportion 
the size of the compensators required to maintain the balance. 

652. Motor Transformers Running and Feeding in Series. — 
An ingenious method of utilizing motor transformers has been de¬ 
vised by Mr. Bernstein. While usually applied to straight currents, 
it is also applicable to alternating currents. The method consists in 
laying from the central station a series circuit receiving power from 
a single generator, including in the circuit any desired number of 
motor transformers. One striking peculiarity of this system is the 
arrangement of the engine, or other prime mover, without any speed 
regulator for controlling changes in load ; the engine being allowed 
to run at any desired speed up to a certain predetermined maximum, 
which will correspond to a delivery of the highest voltage to be 
obtained from the generator. 

The motor transformers are those having double windings on the 
armatures, the motor side of each transformer being connected in 
series with the primary line, so that the whole number forms a group 
of series motors operating upon the station circuit. The other wind¬ 
ings of the armature are arranged to be in series with the receivers 
of each separate circuit, and are proportioned to supply the requisite 
number of receivers that may be expected upon each of the secondary 
circuits. The number of customers upon the secondary circuits may 
be increased or diminished at pleasure, by simply short-circuiting the 
apparatus of the customer, which is for the time being thrown out of 
service, by this means rendering the various receivers independent 
of each other. The general outline of this circuit is shown in Fig. 269. 


494 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


In this design it is apparent that neither the motor transformers 
nor the generators and engine at the station require any special 
supervision, the whole plant being entirely self-regulating. The effi¬ 
ciency of the design is low as is common in series circuits, unless 
the plant can be arranged to operate essentially under a constant full 
load. It is also noteworthy that there is no need of automatically 



regulating the position of the brushes on the series machines, as is 
customary ; for inasmuch as the current is constant in both armature 
circuits, regulation is accomplished entirely by a variation in the 
speed of rotation of the various armatures of the motor transformers. 

653. High and Low Potential Distribution from the Same 
Station. — M. Rechniewski has devised the following ingenious 



Fig. 270. High and Low Potential from One Station. 


method for delivering two different potential values at one station. 
The generators are arranged at A, Fig. 2T0, in such a manner that 
part of the dynamos may operate in parallel upon the circuit BC, 
which may be supposed to feed a group of 110 volt lamps placed 
close to the station. The remaining dynamos are placed in series 
with the first machines, giving a 220 volt circuit to be used, for exam- 































MISCELLANEOUS METHODS. 


495 


pie, at a considerable distance from the plant. At D a motor trans- 
foi mer is placed, so designed that in connection with the circuit D E 
it shall absorb 110 volts, leaving 110 from the 220 of the circuit to 
pass the lamps at E. From the other side of the motor transformer 
at F, a 110 volt current is obtained, which is also passed to the lamps 
at E. By this ingenious device, only half of the energy undergoes 
transformation, and the advantages of a high potential with a mini¬ 
mum loss of efficiency is secured. 

654. Leonard’s System of Motor Regulation. — For the spe¬ 
cial case of electric motors, operating under wide variations of load 
and speed, particularly in instances where the direction of rotation 
is frequently reversed, Mr. H. W. Leonard proposes the following 
method of regulation, depending upon the principle that the poten- 


E C 



tial at the motor terminals should be proportional to the desired 
speed, while the current should vary as the torque or twisting mo¬ 
ment required. The method is diagrammatically shown in Fig. 271, 
in which B is the motor, and A and C two generators, the office of 
the generator C being simply to excite the fields of the motor B and 
the generator A. The field currents are controlled by the rheostats 
D and E. The armatures of the generator and motor are directly 
connected. So long as the generator A is operated at a constant 
speed, the electro-motive force generated will be proportional to the 
strength of its field, which is controlled by the rheostat D. The 
field of the motor being constant, the speed of its amature will de¬ 
pend upon the applied electro-motive force ; and, hence, this speed is 
also controlled by the rheostat D. The current will automatically 
vary proportionally to the torque exercised by the motor armature, 


















































496 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


and the efficiency will be constant and independent of both speed 
and torque. Reversal of rotation is readily accomplished by a rever¬ 
sal of the field current. This method has been very successfully 
applied to the operation of elevators and to similar pieces of ma¬ 
chinery. 

655. Accumulators. — The discovery of the storage battery two 
decades ago seemed to present to electricians a means whereby 
electrical energy could be stored and preserved to meet future de¬ 
mands. It is difficult to say why the application of the storage bat¬ 
tery to central station use has not in this country reached a wider 
development, for in Europe there are very many plants that owe 
their commercial success essentially to combinations of storage bat- 

•t 

teries and dynamo machinery. The central station engineer is com¬ 
pelled to meet and combat two difficulties. If the plant be so 
designed as to be sufficient for the maximum load, it will, for a very 
large proportion of the time, run under so light a load as to be 
exceedingly inefficient, thus largely increasing the cost of the pro¬ 
duction of energy. If, on the contrary, the station be so arranged 
as to be fairly loaded during the majority of the time of action, it will 
fail in capacity throughout the periods of heavy load. As an adjust¬ 
ment to the conditions of varying load, central stations are usually 
so planned as to consist of a number of units which may be thrown 
on and off to accommodate the station to the demands thrown upon 
it. While this is a partial solution of the problem, so far as the 
working efficiency is concerned, it necessitates the investment of a 
very large amount of capital in machinery, which is necessarily idle 
for a great portion of the time. 

656. Examining Diagram No. 11, Fig. 262, it will be seen that 
the mean current of the St. James Station for the twenty-four hours 
of November 21, was about 1,200 amperes, while the maximum cur¬ 
rent rose to nearly 3,000 amperes. Could some means be provided 
that the station might run uniformly during the twenty-four hours at 
a steady load, the superfluous energy not needed in the lines dur¬ 
ing the greater part of the day being conserved and rendered avail¬ 
able during the hours of heavy load, it is apparent that the initial 
capital invested in the station could be reduced in proportion to 
the output required, while the machinery could be so proportioned 
as to constantly run at its point of maximum efficiency. The ac- 


MISCELLANEOUS METHODS. 


497 


cumulator provides precisely the means needed. By arranging the 
station so that the dynamos shall have a capacity, for the average 
load called for, with such an accumulator capacity as will enable 
the dynamos, plus the accumulators, to serve the maximum cur¬ 
rent, it is evident that the station may be continuously operated 
during the whole of each twenty-four hours, at its most economi¬ 
cal load ; the surplus current during the hours of light load flow¬ 
ing into, and being conserved by the accumulators, while, during 
the hours of heavy load, the accumulators discharge themselves 
into the line, supplementing the dynamo output to the extent of 
rendering it possible for the station to meet the demands of the 
consumers. 

657. The recent perfection of the storage batteries indicates 
such an improvement in efficiency and in the life of the battery 
plates as to make this method of equalizing the central station 
load an exceedingly promising one. Reports from Europe indi¬ 
cate in the Hanover Station a battery efficiency, for an entire year, 
of 78.4 per cent. Several plants in Germany give 78 per cent. 
The Fifty-third Street Edison Station in New York reports a daily 
efficiency as high as 85 per cent, and the Crompton-Howell Com¬ 
pany in London are prepared to guarantee 85 per cent upon all 
the batteries supplied by them. Nearly all authorities admit that 
75 per cent may be constantly realized, and that, under favorable 
conditions, 80 per cent or more may be expected. When it is 
considered that, as the batteries are only used to supply a fraction 
of the entire station output, usually from 80 to 50 per cent of the 
full current demanded of the station, the loss entailed by the lack 
of battery efficiency upon the whole station output is compara¬ 
tively a small quantity. In the Hanover Station, for example, 
where the battery output is very high, being 54 per cent of the 
whole station output, the loss entailed by the battery is so com¬ 
paratively small that the station averages an efficiency of over 
91 per cent, a very much higher average than can be attained 
by stations operating solely by mechanical means, owing to the 
loss entailed by running the plant for a large number of hours 
in an unloaded condition. 

658. The electrical railway problem would seem to receive 
from the storage battery an exceedingly happy solution, for, from 


498 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


the station curves already given in Chapter X., the irregularity of 
load upon a railway station is seen to be exceedingly severe and 
irregular. It may be almost confidently stated that no electrical 
railway plant can operate at its point of maximum efficiency, on 
account of sudden and extreme variations of load to which the 
station is subjected. To, therefore, supply railway stations with 
a suitable accumulator plant, which should allow engines to 
run at a reasonably constant and uniform load at the point of 
maximum efficiency, and allow the battery to make up in the line 
deficiencies of the current supplied by the dynamos, would cer¬ 
tainly be attended with the happiest results. Already railway 
station managers in this country are seriously considering the 
increasing of station capacity by means of accumulators, and the 
wide adoption of this method in the near future seems to be a 
foregone conclusion. 

659. Sub-Station Accumulators. — The accumulator may be 
used in a manner similar to the motor transformer by being located 
at a number of sub-stations which may correspond to centers of 
distribution. The employment of accumulators in this manner 
forms one solution of high potential transmission, by allowing 
the generating-station to work at high pressure, the batteries in 
the sub-stations being arranged to be charged in series, while they 
are discharged into the consumers’ circuits in parallel. In this 
way the batteries at the sub-stations may be charged under a 
very high potential with a small quantity of current, and yet serve 
a large territory at the ordinary lighting voltage with a large cur¬ 
rent. Inasmuch as the batteries do not need constant attention, 
it is practical to place the care of a number of sub-stations in the 
hands of a single assistant, who may visit each station at differ¬ 
ent periods of the day, giving each of the separate batteries such 
supervision and maintenance as may be necessary. In this respect, 
the accumulator is an improvement over the motor dynamo, for 
the latter almost necessitates the constant presence of an attend¬ 
ant. On the other hand, however, the cost of battery maintenance, 
including the deterioration of the plates, the losses of exciting fluid, 
etc., are considerably larger than the maintenance expense entailed 
by motor generators ; for, while the present battery manufacturers 
are prepared to give five or even ten years’ guarantee for the per- 


MISCELLANEOUS METHODS. 


499 


manence of their goods, the life of a motor dynamo, the commu¬ 
tators and brushes alone excepted, is practically without limit. 
Accumulator stations may be designed either on single or multiple 
wire systems, for either the primary or secondary conducting sys¬ 
tems, or both. 

660. Accumulator Distribution. — The more customary meth¬ 
ods of distribution by means of accumulators are indicated in Figs. 
272 and 273. In the first illustration, the batteries B B B B are 
arranged in series along the entire line, the generator feeding all 




of the sets. The receivers are taken off in four parallel circuits, 
each one of the batteries being of sufficient voltage to adequately 
supply all of the customers. A similar arrangement is indicated in 
the latter illustration, with the simple modification that in this case 
the secondary consumers circuits are laid out upon the three-wiie 

system. 

661. Regulation by Means of Accumulators. — A very conven¬ 
ient application of the accumulator system is in the accomplishment 
of the regulation of voltage to be delivered at the end of the feeders, 
by planning the battery so that there are a sufficient number of cells 



























































500 


TIIE ELECTRICAL TRANSMISSION OF ENERGY. 


to make up for the fall of pressure in the feeds, and arranging the 
extra cells in such a manner as to be readily thrown in and out of 
service by means of an appropriate switching apparatus. 

Thus the accumulator forms an exceedingly valuable and simple 
method of regulating the potential delivered at the ends of the feeder 
system. As the load is thrown on the plant, the increasing current 
causing a drop at the ends of the feeds, additional cells may be 
switched into the circuits in series, thus increasing the potential 
precisely in accordance with the demands of the line. 

662. Transformers. — The devices for rendering high potential 
circuits available, that have so far been considered, are those applica¬ 
ble to straight currents. The alternating current presents a solution 
of the problem, at least so far as lighting-circuits are concerned, in 
an exceptionally beautiful manner. The motor transformer and the 
accumulator are dynamic pieces of apparatus, which constantly re¬ 
quire more or less supervision, and from this cause are sources of 
considerable expense. With the alternating system, the principles 
of induction may be so utilized as to enable the plant to distribute 
electrical energy over wide areas with the greatest economy, without 
the interposition of machinery needing supervision. In the case of 
the motor transformer, a rotating armature is supplied with a high 
potential current through the fine windings, and distributes a low 
potential current through the coarse windings. In this case, the 
cutting of the magnetic lines is accomplished by the rotation of the 
armature. In the case of the alternating currents, no dynamic rota¬ 
tion is necessary, as the wave form of the current itself supplies the 
necessary changes in the magnetic field. The transformer in its 
essential parts consists merely of an iron core surrounded with two 
coils of wire, a fine coil and a coarse coil. The fine coil is connected 
to the primary line, receiving electrical energy at a high potential, 
while the coarse wire coil is in communication with the lines of the 
consumers. The alternations of the primary current cause magnetic 
alternations in the core, thus inducing a secondary current in the 
coarse wire coil. Without serious error, it may be stated that the 
transformation thus effected is in proportion to the ratio of the num¬ 
ber of turns of wire in the coarse coil to the number in the fine coil. 
If the primary wire is operated under 2,000 volts, and 100 volts is 
required in the consumer’s circuit, the turns on the two coils in the 


MISCELL A NE O US ME THODS. 


501 


transformer will be in the proportion of twenty to one. The advan¬ 
tage of the transformer lies chiefly in the fact that it needs abso¬ 
lutely no supervision. Once built and placed in position, it needs no 
further attention, unless injured from some exterior cause, but will 
go on performing its part of the service for an indefinite time. 

663. Economy in the Conductor. •— It is easy to calculate the 
economy that may be made in the circuits. Let IV be the energy 
in watts to be transmitted between the generating station and the 
receivers. Supposing / to be the current, and E to be the difference 
of potential, and w the energy which is lost in the line, equal to a 
certain fraction m of IV If direct current distribution is used, the 
resistance of the line becomes, — 

X = (247) 

and also, w = ?nEI = RE 1 . (248) 

Suppose, on the contrary, that the same energy be transmitted 
under a difference of potential K times more elevated and a current 
K times more feeble. Under these circumstances — 


w — R 



(249) 


from which it follows that R = K-R, and therefore, as the length 
of line remains the same in the two cases, the same relations exist 
between the relative amounts of copper that are necessary for the 
appropriate circuit. For example: energy transmitted under a 
potential of two thousand volts requires four hundred times less 
copper for the same line losses than is needed under a transmission 
of one hundred volts ; and conversely, with a tension of two thousand 
volts, it is possible to make the circuit four hundred times as long, 
with the same loss, as would be required for a potential of one 
hundred volts. Thus it is evident that raising the pressure of the 
energy will permit a distribution over a very much greater space. 
For an aerial line, the economy indicated is usually attainable; but 
when the circuit is placed underground, the full saving can very 
rarely be realized, for in the latter case a large proportion of the 
expense of line is required in the construction of the subway. Under 
these circumstances, a saving in the weight of the conductors will 
only decrease the total cost of the circuit by a smaller proportion, 



502 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


inasmuch as the cost of the subway will remain the same. It 
should also be recollected that the saving in the cost of the circuit 
is also offset by the expense made necessary by the use of trans¬ 
formers •— an outlay of capital that is necessary to incur when the 
plant is first established. 

664. There are three possible ways in which transformers may 
be operated. 

First . All of the primaries may be in series with the receivers 

on the secondaries in parallel. 

Second. Both the primaries 
and the receivers on the secon¬ 
daries may be in series. 

Third. The primaries and 
the receivers on the secon¬ 
daries may both be in parallel. 
These methods are indicated 
diagramatically in Fig. 274, 
Nos. 1, 2, and 3. 

According to the first sys¬ 
tem, if any receiver be put into 
or out of commission, the re¬ 
sistance of the secondary cir¬ 
cuit will be correspondingly 
diminished or increased. This 
will proportionally vary the im¬ 
pedance of the primary circuit; 
and the current therein will be, 
in a like manner, varied in 
quantity. Such a system cannot be made self-regulating ; and, if 
used, must depend entirely upon manual regulation at the station. 

665. In the second system, with the receivers arranged in 
series, a practical working arrangement is obtained, if the primary 
current is derived from a constant current alternator having the 
ability (by compound winding or automatic regulators) of maintain¬ 
ing a constant current for considerable variations in the impedance 
of the primary circuit. This arrangement has received quite a wide 
development in arc-lighting plants operated by alternating currents, 
the customary design being indicated in Fig. 275. 



No. 1. TRANSFORMERS ARRANGED IN SERIES, 
WITH LAMPS IN PARALLEL. 



NO. 2. TRANSFORMERS ARRANGED IN SERIES, 
WITH LAMPS IN SERIES. 



No.3. TRANSFORMERS ARRANGED IN PARALLEL, 
WITH LAMPS IN PARALLEL. 

Fig. 274. Transformer Circuits. 

































503 


MI SC EL L A NE O US ME THODS. 

666. The third method is the one most usually employed ; for, 
if the transformers are designed with sufficient impedance in the 



primary circuit to practically block out all current, when the second¬ 
ary is open, the system then becomes almost perfectly self-regulating. 

667. Usually, however, the transformer service is installed as in¬ 
dicated in Fig. 276. With this arrangement, the transformers may 



be regarded, in their relation to the central station, precisely as if 
they were the receivers themselves, and the distribution studied 
and designed in accordance with the principles for direct currents. 



















































































































504 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


Where the area to be covered is very large, or the amount of energy 
transmitted great, the feeder and main system finds economical 
application, as indicated in Fig. 277. 

668. The transformer system further presents great flexibility 
in the distribution from the secondary circuit. Where a large 
number of receivers are to be supplied at a single location, the trans¬ 
formers may be banked, with their secondaries in parallel, as shown 
in Fig. 278. Contrariwise, if higher potential be desired to over¬ 
come the resistance of long interior leads, the secondaries may be 
placed in series, as in Fig. 279, thus doubling the potential of the 



Fig. 277. Feeder and Main System with Transformer. 


individual transformer. Finally, the service leads may be arranged 
upon a multiple-wire system, the transformer secondaries being 
arranged in series, and appropriately connected with the inter¬ 
mediate wires. For three-wire distribution the arrangement is 
indicated in Fig. 280. Even with the best proportional trans¬ 
formers, there is a small unavailable consumption of energy due to 
I 2 R losses and hysteresis. When operating under a large load, the 
percentage of energy thus wasted becomes insignificant ; but, during 
the hours of light loading, these wastes rise to formidable propor¬ 
tions. From this aspect, the common method of installing a separate 
transformer to serve the wants of each consumer is exceedingly 









MISCELLANEOUS MET/LODS. 


505 


detrimental to the attainment of high service efficiency. The trans¬ 
former supplied to each customer must have sufficient capacity to 
carry the maximum load ever desired. Necessarily, even during the 



Fig. 278. Wiring for Transformer Secondary Circuits. Secondaries in Parallel. 

daily hours of maximum loading, the transformer will be operating 
uneconomically at a light load. This is particularly the case in 
residence districts, where each individual house must have a possible 
transformer capacity sufficient to provide for occasional fetes , while 



Fig. 279. 

Wiring for Transformer Secondary Circuits. 
Secondaries in Series. 


Fig. 280. 

Wiring for Transformer Secondary Circuits. 
Secondaries on Three-Wire System. 


the daily load is but a fraction of the occasional demand. A great 
improvement in efficiency may be attained by designing the trans¬ 
formers to serve groups of buildings, as it is evident that special 
loading will rarely simultaneously occur to more than one customer 




































































































50G 


tiie electrical transmission oe energy. 


in such a group. Thus the average load will much more nearly 
approach a full load. 

669. If the transformer is located to feed a subscriber, or group 
of subscribers, it is most appropriately placed at the center of 
gravity of the system of receivers that it is expected to feed. Inas¬ 
much as it is not advisable to allow a high-tension circuit to enter 
the houses of the subscribers, this condition cannot always be 
strictly followed. 

Theoretically, the transformer system becomes the most econom¬ 
ical under the following conditions : — 

First. A supply to the transformers by a primary circuit served 
by a system of feeders. 

Second. A secondary circuit from the transformers supplying the 
receivers by a multiple-wire system. 

670. The Efficiency of Distribution by Isolated Transform¬ 
ers. — The greatest offset to the use of the transformers lies in the 
low efficiency which is to be obtained when the instruments are oper¬ 
ated for a greater part of the time under a light load. No matter to 
what extent the perfection of the transformer may be carried, the 
output is never quite equal to the total amount of energy which is 
supplied to it. For example, supposing the output of a transformer 
under full load to be 95 per cent of the energy supplied to it, there 
remains 3 per cent to be lost by hysteresis and Foucault currents, 
and 2 per cent due to heating of the circuits. The loss by hysteresis 
is continual, and is entirely independent of the loading placed upon 
the transformer. The heating-losses, however, diminish in propor¬ 
tion to the load. Now, with all the transformers at work during 
twenty-four hours of each day, assuming, as a fair estimate, that they 
will operate for two hours under a full load, four hours under a 
half load, and during the remainder of the time under no load, the 
mean daily efficiency then becomes easy to calculate. Assuming 
the efficiency of the transformer to be 95 per cent at full load, 
the demand on the station during the twenty-four hours is as 
follows : — 


3 per cent during 18 hours 
50 per cent during 4 hours 
100 per cent during 2 hours 


= .54 
= 2.00 
= 2.00 


Total 


4.54 







MISCELLANEOUS METHODS. 507 

The output which the transformer gives to the secondary circuit 
is — 

0.00 during 18 hours.=0.00 

0.46 during 4 hours.=1.84 

0.95 during 2 hours.=1.90 

Total . 3.74 


The total efficiency is — 

3.74 / 4.54 = 0.825. 

671. Now, admitting the above excellent conditions, and allowing 
an annual operation covering 1,500 hours, the employment of the 
transformers reduces, in the above proportion, the amount of elec¬ 
trical energy which can be utilized in the secondary circuits. If, on 
the other hand, the transformers operate for two hours under full 
load, and only two hours under a half load, the efficiency is low¬ 
ered 4 per cent. From these figures, it is evident that great care 
should be exercised in the selection and design of a plant. If, for 
example, it is practical, in a mountainous region, to take advantage 
of a waterfall, where the power costs little or nothing, and where the . 
expense of installation is moderate, it is evident that the transformer 
system may be used with great economy and advantage. On the 
other hand, in cases where natural power is not available, as, for 
instance, in the center of a crowded city, and it becomes essential to 
use steam power, the losses experienced in the transformer may 
entail a coal expense which is equal to, and often far greater than, 
the interest and depreciation of a large conducting system. 

672. Transformers Arranged as Sub-Stations. — In order to 
avoid the loss of energy due to light loading of the transformers, 
they may be grouped in sufficient numbers at a single spot, thus 
forming an auxiliary station. It is a simple matter here to install 
appropriate switches, by means of which the transformers may be 
thrown out of circuit during the idle hours of the day, when the load 
is comparatively light, and may be successively thrown into action as 
the load increases. This operation is usually a manual one, thus 
requiring the presence of an attendant during a part of each day. 
If, however, the sub-stations are so arranged that the attendant can 
proceed from one to the other successively, to cut in or out the vari¬ 
ous instruments, a single attendant will be sufficient. Many pieces 








508 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


of apparatus have been proposed to throw the transformers in and 
out of circuit automatically ; and while, on the one hand, it is doubt¬ 
less possible to accomplish this, it will be necessary to have much 
greater experience with automatic machines of this description before 
full confidence and reliance can be placed upon them. The location 
of the auxiliary stations should be studied with equal care to that 
which is devoted to the selection of the site of the main plant. The 
secondary system of mains and feeders also becomes a matter of 
care in design, and requires even greater attention than in the case 
of house-to-house transformers. The three-wire system now becomes 
particularly applicable, in view of the economy to be derived in the 
conductors, especially as the auxiliary stations are designed to feed a 
much larger territory. With the auxiliary station arrangement, it 
becomes practically advisable to feed each sub-station by means of 
a single pair of mains extending from the main generating-plant. 
Under these circumstances, particular care should be taken to con¬ 
nect the auxiliary stations among themselves in such a manner that, 
in case of any accident to a pair of mains from the central station to 
a particular auxiliary station, the service may not be interrupted, but 
that the incapacitated sub-station may be fed by a roundabout circuit 
through the other auxiliary plants from the central station. A sepa¬ 
rate dynamo may be arranged to connect each set of mains to its 
corresponding transformer, or set of transformers. However, from 
an economical standpoint, it is usually preferable to unite the genera¬ 
tors among themselves, in order to make them operate under the 
best possible conditions of loading. It should be noted here that 
one of the largest English central stations has preferred to employ 
a small number of machines, graded in size in such a way that one 
after the other may be thrown in or out of service, so as to keep the 
machines that are at work constantly under full load, and, therefore, 
operating at their point of maximum economy. 

673. Polyphase Transmission. — Electrical distribution, as ae 
complished by the ordinary alternating current, can, as yet, only be 
considered to be entirely successful when applied with currents of 
reasonably high frequency to incandescent lighting. The carbons in 
arc lamps operated by alternating current, being equally consumed, 
the reflecting power of the crater formed in a direct current lamp is 
lost, and considerable illuminating efficiency sacrificed. By increas- 


MISCELLANE O US ME THODS. 


509 


ing the size of the upper carbon, and by means of reflectors, alternat¬ 
ing current arcs are greatly improved ; but they are hardly regarded 
as quite equal to those of direct current installations. With low fre¬ 
quencies, unsteadiness in both arc and incandescent lamps becomes 
quite noticeable, while with high frequencies the impedance and 
capacity, especially of long circuits with large currents, become 
almost unmanageable factors. For power distribution in any form, 
the plain alternating current is particularly disadvantageous, for as 
yet no thoroughly successful alternating current motor has been 
devised. The common synchronizing motor must be started by 
auxiliary apparatus, and brought into step with the generator, before 
the load is applied, and then can only operate under almost constant 


N 


S 


Fig. 281. Diagram of Triphase Armature Connnections. 



conditions of loading. In the search for the ideal alternating cur¬ 
rent motor, electricians have evolved the polyphase system, which, 
particularly for power transmission, presents especial advantages. 

674. For a proper comprehension of the polyphase systems, 
some consideration of the way that electric currents are generated 
is necessary. Suppose, in Fig. 281, N and S be the poles of a gen¬ 
erator, between which a gramme ring armature is revolved. If the 
opposite diameters of the armature be connected by means of brushes 
to two collecting-rings, an undulating current is obtained that may be 
represented by the line AAA, Fig. 282. Suppose, instead of this 
arrangement, that three coils, distant 120 degrees from each other, 
are taken as indicated in Fig. 281, and brought to three collecting 
rings, a , b , c. In every revolution of the armature each coil will 
become the seat of an undulatory current, precisely similar to the 









510 THE ELECTRICAL TRANSMISSION OF ENERGY. 

one already cited, excepting that, as the coils are separated by 120 
degrees, the phases of the three currents will lag behind each other 
by a similar amount. These currents are shown in big. 283. Evi¬ 
dently any number of coils could be thus arranged, giving rise to a 
corresponding number of different phased currents. To avoid im¬ 
practicable complexity of circuits, distribution has, so far, been 
confined to diphase and triphase currents. 1 he diphase current is 
given in Fig. 282, AA and BB being the two waves, separated by 



Fig. 282. Diagram of Diphase Currents. 


one quarter of a period. Diphase transmission may be accomplished 
by providing two separate circuits, requiring four wires, one for each 
wave. It is possible to economize conducting material, by providing 
a common return conductor for both waves ; but as is indicated by 
the line CC in Fig. 282, giving the algebraic sum of the two cur¬ 
rents, the common return must be a larger conductor, thus destroy¬ 
ing the symmetry of the circuit. Returning to Fig. 283, the three 
currents, lagging by one-third of a period each, have equal effective 
intensities, with the further advantage of having their algebraic sum 
constantly equal to zero. Three equal and symmetrical conductors 








MISCELLANE 0 US ME THODS. 


511 


will then serve to transmit triphase currents. The connection be¬ 
tween the generator, the circuit, and the receivers, may be made in 
two ways, by what is called “star connection,” or by “triangle 
connection,” diagrammatically indicated in Fig. 284. The star con¬ 
nection possesses the advantage, that, with it, it is possible to 
connect the common center of the three circuits to a fourth, or neu¬ 
tral, wire, and to arrange the receivers working as simple resistances, 
such as incandescent lamps, between the neutral wire and either of 
the other three. The three sections of the generator now act each 
as an ordinary alternating current dynamo, without disturbing reac¬ 
tions upon other parts of the system. The triangle mode of connec¬ 
tion does not permit of this latitude. The famous Lauffen-Frankfort 
transmission circuit employed triphase station apparatus, the circuit 
being diagrammatically indicated in Fig. 285, in which GS is the 
generating-station, a , b , and c, the three leads to a step-up transfor¬ 
mer T, RS is the receiving-station with step-down transformer T, 
and the three main leads, a, b, and c , with the neutral wire NW. It 
will be noticed that the center of the “ star connection,” to which the 
neutral is attached, is grounded both at the generating-station and at 
the receiving-station, on the low potential side of the transmitting 
system. 

675. To determine the difference of potential existing between 
any two wires upon a triphase system, it is easy to see, by an exam¬ 
ination of Fig. 283, that if E is the electro-motive force between 
the two wires, and e is the difference in potential between any wire 
and the neutral point, then, — 

E = e 2 sin 60° = 1-732 (250) 

With a triphase system it is, therefore, possible to establish 
six different circuits, each of which may be conveniently used for 
incandescent lighting. 

Diagrammatically, this arrangement is shown in Fig. 286. The 
common center, or neutral point of the three wires, is represented at 
O. From the terminals of the three wires, a , b, and c , three mains 
extend, across which lamps may be placed. The neutral wire is 
shown by the dotted lines ONW extending from the center of the 
three wires. Between the neutral wire and any one of the external 
leads, as a, b, or c , lamps may be also placed. It must be noted that 


512 


THE ELECTRICAL TRANSMISSION OF ENERGY. 







Fig. 285. The Lauffen-Frankfort Circuit 














































MISCELLANEOUS METHODS . 


513 


the voltages between the three wires, ac and ab, or cb, and between 
any of the wires a , b , c, and the neutral wire, will vary in the propor¬ 
tion above indicated ; namely, as 1 to 1732, and, therefore, on each 
of the different circuits here represented different voltage lamps 
must be used. 

Incandescent lamps arranged between each of the three wires 
a, b, c, and the neutral wire, possess greater independence than those 
which are situated between either of the three wires ab , ac , or cb. 
The lamps which are installed in connection with the neutral wire 
possess complete independence of each other, and also in reference 
to the three main circuits. In this case each of the three circuits 
acts independently of the other, the entire system behaving as if 



there were three separate and independent generating-stations, each 
lagging behind one another one-third of a period ; on the contrary, 
the lamps which are installed between the circuits ab , ac , or be , are 
more or less inter-dependent, as it is found that, when the three cir¬ 
cuits are unbalanced, considerable difficulty in regulation arises. 

676. As yet, triphase distribution has not been very extensively 
applied to arc-lighting, as it is probable that, with the present lamps, 
difficulties due to self-induction in the regulating mechanism of the 
lamps might be encountered. The principal advantage, however, of 
the triphase system is obtained when it is applied to the operation 
of electrical motors. Referring to Fig. 287, a typical dynamo for 
triphase work is shown. Here the machine consists of a shaft 
carrying a gramme ring armature, placed so as to rotate between 
the two field magnets. The shaft carries a commutator at B, and 







































514 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


three collecting-rings, b, and c , the connections to the armatuie 
being separated from each other by 120 degrees, each part being, 
as indicated in the illustration, carried to its appropriate collecting¬ 
ring. Such a machine as this is extremely flexible in service. 

First. By applying power to pulley A, making the armature turn 
mechanically, a continuous current may be obtained from the com¬ 
mutator B. 

Second. By supplying a continuous current to the commutator B, 
the dynamo is operated as a motor, and mechanical power may be 
obtained from the pulley A. 


a b c 



Third. By applying mechanical power to the pulley A, turning 
the armature, and, instead of collecting the current at the commuta¬ 
tor B, collecting it by the rings a, b, and c, a triphase alternating 
current generator is obtained, being self-excited by a current derived 
from the armature by the commutator at B. 

Fourth. By supplying triphased alternating currents to the col¬ 
lecting-rings a, b, and c, a synchronous alternating current motor is 
obtained, and mechanical power may be derived from the pulley A. 

Fifth. If a continuous current be supplied to the commutator B, 
a triphased alternating current may be obtained from the collectors 
a , b , and c\ thus, in this case the dynamo acts as a motor trans¬ 
former, transforming a continuous current to a triphase alternating 
current. 

















































MISCELLANEOUS ME THODS . 


515 


Sixth. If a triphase alternating current be supplied to the col¬ 
lectors a, b , and c, a continuous current may be obtained from the 
commutator B, the dynamo now operating as a motor transformer, 
changing a triphase alternating current into a continuous current. 
While the preceding example of a dynamo machine presents an 
interesting illustration of the interconvertibility of electrical currents 
and mechanical forces, the chief interest in a triphase system lies in 
its application to non-synchronous motors, or those having revolving 
magnetic fields. In the previous instance it is shown that a triphase 
current is only connected with the armature of the motor and not 
with the fields. If, on the contrary, the triphase current be arranged 
to excite the fields of the motor, it is apparent that the sign of the 
field will vary, as the wave entering the field coils, and, in a multi-polar 
machine, the magnetic field will evidently rotate around the ring 
forming the magnetic circuit, precisely in accordance with the suc¬ 
cessive waves entering from each of the three wires. In a non- 
synchronous motor the armature consists of an electrical circuit 
closed upon itself, and in no electrical connection with the line 
circuit, or the magnetizing fields of the machine. The valuable 
properties of the non-synchronous revolving field motor consist in 
the ability of the machine to start itself and bear wide changes in 
loading, without manifesting any of the injurious qualities that are 
usually found in the ordinary synchronous type of machine. The 
efficiency also of the non-synchronous motor is quite high, usually 
ranging considerably over 90 per cent. 

677. While alternating currents lend themselves extremely 
readily to long distance transmission, it is evident, from what pre¬ 
cedes, that it is difficult to design a plant for all round service. 
While the plain alternating current is advantageous for incandes¬ 
cent lighting, it is badly adapted to the distribution of power; and, 
on the other hand, while a triphase system lends itself especially 
to power transmission, it is not so well adapted for incandescent 
lighting, especially under circumstances where it is necessary to 
connect the lights across three wires of the triphase system. At 
present, the best design for long distance transmission seems to 
lie in the adoption of a di- or triphase system for the main trans¬ 
mission, arranging the receiving-station with motor transformers, 
from which direct currents may be obtained for local distribution, 


510 


THE ELECTRICAL TRANSMISSION OE ENERGY.\ 


for operation of stationary motors, and the supply of arc and 
incandescent lighting. 

678. Long Distance Transmission. — Ever since the classical 
experiments of Marcel Deprez in 1882, demonstrating the rever¬ 
sibility of dynamo machinery, the problem of the transfer of large 
amounts of power over long distances has been a favorite study 
of the electrical engineer. 

Every waterfall has been a temptation to the engineer, in the 
mists of which the enthusiasm of the scientist has seen possible 
golden returns derivable from the transmission of the energy 
therein developed to a ^commercial center. Chiefly, the long dis¬ 
tance problem is one of station machinery, and, in this respect, 
transcends the scope of the present manual; yet the subject is one 
of so great importance, that a brief reference, particularly directed 
to the line problems arising in long distance transmission, seems 
essential. 

679. In order that a long-distance plant may be commercially 
successful, four requisites are essential. 

First. There must be available water-power, or other source of 
power, by means of which the initial production of energy can be 
very cheaply made. 

Second. The plant necessary for the utilization and the trans¬ 
mission of the power must be installed with a reasonable outlay 
of capital. 

Third. Transmission must be effected at sufficiently high poten¬ 
tials, so that interest and depreciation in the cost of the line and cost 
of energy lost by transmission shall not too greatly augment the 
cost of the power delivered at the receiving-station. 

Fourth. A reasonable market must exist for the disposition of 
the energy from the receiving-station. 

680. Usually the cost of improvement of water-powers and 
the cost of the generating-plant and circuit are so great that, unless 
large amounts of energy can be obtained at a particularly low ini¬ 
tial expense, the plant does not become a commercial success. It 
has been considered impracticable to build direct current apparatus 
at sufficiently high potentials to warrant the transmission of energy 
over lines of considerable magnitude. The difficulties encountered 
in the construction of direct current generators operating under 


MISCELLANEOUS METHODS. 


517 


potentials of more than three or four thousand volts has, so far, 
been found too great to permit of their use in long-distance trans¬ 
mission. Experts are, at the present time, not wanting who feel 
confident that direct current apparatus can be produced which shall 
be capable of operating at much higher electrical pressures; but 
whether this prediction shall prove to be true, especially with the 
heavy currents that must necessarily accompany a distribution of 
magnitude, the future only can decide. All of the long-distance 
transmission plants now in existence, with hardly an exception, have 
been constructed to embrace the use of alternating current appara¬ 
tus. The usual arrangement of the plant is diagrammatically shown 



in Fig. 288. Here M is the water-wheel, or other prime mover, 
from which energy to drive the alternating current generator A 
is obtained. This dynamo is usually a machine operating at quite a 
low electrical pressure, frequently not higher than 50 volts. This 
machine is connected with a step-up transformer 1\ , the office of 
which is to raise the voltage of the generator to any desired quan¬ 
tity, for transmission through the circuits II, II. Between the 
step-up transformer and the receiving-station T 2 the line extends, 
forming the secondary circuit of the first transformer T x and the 
primary circuit of the second transformer T 2 . This latter tians- 
former is a step-down transformer, the office of which is to reduce 
the pressure delivered by the line to such a voltage as shall be 
convenient for distribution and utilization in any desiicd way, such 











































518 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


as the operation of motors, or the feeding of an illuminating circuit 
(as indicated in the diagram). The secondary circuit of this trans¬ 
former forms the distributing circuit of the plant. This is the 
general design of plants for the Electrical Transmission of Energy, 
and in no other direction has electrical engineering advanced more 
rapidly. In the United States installations aggregating 300,000 
H. P. are now (1898) delivering thousands of horse-power over dis¬ 
tances from ten to fifty miles, at potentials of 10,000 volts. What 
voltage can be carried by the transmission-line, and safely handled at 
the generating and receiving stations, has been the debatable ground. 
For urban distribution by alternating currents, employing reducing 
transformers, there seems to be a preference for 2,000 volts. A few 
plants have been installed at 1,000 volts and a number at 3,000 volts. 
In special cases, 4,000, 5,000, and even 6,000 volts have been em¬ 
ployed ; so present practice tends toward the employment of genera¬ 
tors connected directly to the distributing circuits where economical 
transmission may be attained by 6,000 volts. For greater ranges, 
low-potential generators are employed with step-up transformers at 
the generating station, delivering energy at 10,000 volts to the trans¬ 
mission-lines, which end at the receiving stations in step-down trans¬ 
formers. Present experience indicates that 10,000 volts may be 
safely handled, but with higher potentials regard must be given to 
meteorological conditions. Two general designs are now common. 
First: Synchronous generators and motors at the generating and 
receiving stations may be connected by the line and its auxiliary 
apparatus, for the supply of mechanical power. In such an arrange¬ 
ment the line is the ecpiivalent of a long belt. Second: Polyphase 
generators at the generating station may, by means of the line, sup¬ 
ply energy to the receiving station. Step-down transformers and a 
secondary network of conductors may distribute alternating current 
to consumers. Polyphase motors may deliver mechanical power, while 
rotary converters can furnish direct current. Here the receiving sta¬ 
tion becomes the analogue of a completely developed station for sup¬ 
plying electricity. In plants of the first design the line pressure 
may vary with the load, while in the second it is important to secure 
a close regulation at the receiving station. The use of polyphase 
currents in the secondary system demands four wires for the most 
economical conductor design, but avoids the losses in, and the use of, 


MISCELLANEOUS METHODS. 


519 


large rotary machinery ; but the employment of rotary transformers 
allows of the use of three wire mains, and the utilization or contribu¬ 
tion to existing direct-current systems. Thus the best design for a 
transmission-plant lies chiefly in a wise selection of central-station 
apparatus, and so is beyond the scope of this volume ; but a concise 
description of the more important American installations may be of 
value. 

681. The Big Cottonwood Plant (Utah)_The power-plant 

utilizes a waterfall in Big Cottonwood Canon, giving 2,500 available 
H. P. The present installation consists of four 600 H. P. Pelton 
wheels, connected to 450-kilowatt triphase generators, delivering 
alternating current at 60 cycles and 2,000 volts. Step-up trans¬ 
formers raise the pressure to 10,000 volts for the transmission-line, a 
wooden-pole line fourteen miles long to Salt Lake City. The poles 
are 40 feet long, 8" diameter at the top, set 100 feet apart, and carry 
four circuits of three wires, each of No. 2 bare copper, on porcelain 
double-petticoat insulators. The sub-station is provided with step- 
down transformers, reducing the pressure to 2,000 volts for delivery 
to the secondary system. The loss in the line is five per cent. 

682. The Blue Lakes (Cal.) Plant. — The installation comprises 
three TOO H. P. Pelton wheels running under a head of 1,040 feet. 
The wheels are coupled to 450-kilowatt Stanley diphase inductor 
generators delivering current at 60 cycles and 2,400 volts. Step-up 
transformers raise the pressure to 11,000 volts. The pole-line is 39 
miles long, running to the city of Stockton. The poles are 35 feet 
long, red cedar, 6" top, 10" butt, set 6' in the ground. There are 
two circuits of four wires each, of No. 3 B. & S. bare copper. Each 
circuit is on a separate cross-arm, two wires being located on each 
side of the pole. The wires are carried on double-petticoat porcelain 
insulators. A line of barbed fence wire supported on the tops of 
the poles, and grounded at frequent intervals, affords protection from 
lightning. 

683. The Folsom, Sacramento (Cal.), Plant. — The power-plant 
contains four pairs of 30 " McCormick turbine wheels of 1,200 H. P. 
each, coupled to 750-kilowatt General Electric three-phase generators 
delivering current at 60 cycles and 800 volts. Step-up transformers 
deliver energy to the line at 11,000 volts, extending from Folsom to 
Sacramento, a distance of about 24 miles. Cedar poles 40 feet long, 



520 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


16" at the butt, are used, set 105 apart. Each pole carries five 
arms 4" X 4" x 7' long, set 16" apart. Each circuit consists of 
three pairs of No. 6 bare copper wire supported on double-petticoat 
porcelain insulators. The loss in transmitting 3,000 H. P. is 7i per 
cent. At Sacramento a sub-station with step-down transformers is 
designed to deliver currents at 125, 500, and 1,000 volts, that are 
used respectively with three sets of mains. Three 250-kilowatt syn¬ 
chronous motors drive a line-shaft to operate a 200-kilowatt and a 
100-kilowatt, 500-volt railway generators, and three 100-light and two 
75-light arc machines. 

684. The Fresno (Cal.) Plant. — Pelton water-wheels, each devel¬ 
oping 500 H. P. under a head of 1,400 feet, are directly connected 
to General Electric three-phase generators, each of 340-kilowatts 
capacity. Step-up transformers raise the voltage to 11,200 volts. 
The transmission-line carries two circuits, each of three pairs of 
bare copper wire, extends 35 miles to Fresno, ending in a sub¬ 
station with reducing transformers, one to reduce the pressure to 
200, one to 1,000, and one to 3,000 volts ; corresponding to a triple 
distributing system, a four-wire low-tension circuit, a four-wire 1,000- 
volt circuit for light and power, and a four-wire 3,000-volt circuit. 
The sub-station contains two 60 H. P. three-phase induction motors, 
that drive two 80 arc-light machines. 

685. The Helena (Montana) Plant. — The present capacity is 
4,000 H. P., with a possible future capacity of 10,000 H. P. The 
power-house is equipped with American turbine wheels, mounted in 
pairs, each set developing 500 H. P., directly connected to 350-kilo¬ 
watt Westinghouse alternators. Step-up transformers raise the pres¬ 
sure to 10,000 volts. The line consists of four circuits of No. 4 
bare copper wire, two running to East Helena, eleven miles, and two 
circuits to Helena, seven miles. Step-down transformers deliver cur¬ 
rent to the secondary system. Two 175-kilowatt rotary converters 
supply the street railway and two 100-kilowatt motors operate arc 
machines. 

686. The Indian Orchard Plant, Springfield, Mass. — The power- 
plant consists of thirty six inch turbine wheels, of 480 H. P. each, 
with a total equipment aggregating 1,920 H. P. The turbines are 
belted to counter shafting, from which the generators receive power. 
1 he electrical equipment consists of 360-kilowatt diphase alternators, 



MI SC EL LA NEO US ME 1 'HODS. 


521 


operating at 6,000 volts, and delivering current directly to the trans¬ 
mission-lines. At Springfield, diphase synchronous motors receive 
power from the transmission-lines, and drive counter shafting from 
which arc-light and direct-current machines are operated. 

687. The Lowell (Mich.) Plant -The power-house is equipped 

with three 100 H. P. turbine wheels, belted to a counter shaft and 
thence to the generators. The electrical equipment consists of a 
1,000-volt generator (with exciter), of 200-kilowatts capacity, operat¬ 
ing at 133 cycles. Step-up transformers raise the pressure to 10,000 
volts, and deliver it to the transmission-line, extending 18 miles to 
Grand Rapids. At this city a sub-station reduces the potential to 
2,000 volts for the distributing system. The pole-line consists of 
thirty-foot poles six inches top, set 100 feet apart. The circuit con¬ 
sists of four No. 6 bare copper wires placed upon double-petticoat 
porcelain insulators. 

688. The Montmorency Falls (Canada) Plant. — The Montmo¬ 
rency Falls, eight miles from Quebec, afford a water-power capable 
of developing 12,000 H. P., with a head of 275 feet. A generating 
station has been constructed, equipped with Little Giant turbine 
wheels, each of 700 H. P. capacity, connected directly to Stanley 
diphase generators. Each generator has a capacity of 600 kilowatts, 
and delivers alternating currents at 5,200 volts, and a frequency of 
66. From the power-house two pole-lines extend to Quebec. Each 
consists of four No. 0 B. & S. bare copper wires carried upon wooden 
poles, by porcelain insulators. A loss of ten per cent in the line is 
shown. At Quebec step-down transformers reduce the current to 
2,000 volts for distribution. 

689. The Nevada County (Cal.) Electric Power Co. Plant. — 

The power-plant utilizes a fall of 200 feet head on the south branch 
of the Yuba River. Five Pelton wheels of 500 H. P. each are coupled 
to 340-kilowatt diphase 5,000-volt Stanley generators. Current is 
supplied directly to the line at the generating pressure. The line 
consists of two circuits of four wires each, of No. 3 bare copper, ex¬ 
tending four miles ; then one circuit of No. 6 wire extends to Nevada 
City, one mile, and one circuit of No. 3 wire to Grass Valley, four 
miles. Sub-stations with step-down transformers supply the distrib¬ 
uting network, at a pressure of 2,000 volts. 

690. The Niagara Plant. —Turbine wheels are employed, which 


522 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


are set in a slot cut in the rock, to place the wheels nearly at the 
level of the base of the Falls. The wheels are set horizontally, a 
pair being placed upon each shaft, delivering 5,500 H. P., directly 
connected to diphase Westinghouse alternators, delivering current at 
2,200 volts and 25 periods. Upwards of 25,000 H. P. is electrically 
distributed, and about 8,000 H. P. is distributed directly from the 
turbine shafts, and work upon an extension to develop some 40,000 
additional H. P. is nearly completed. The Niagara plant delivers 
energy at three voltages, and under three forms of current. A por¬ 
tion leaves the power-house as diphase alternating current at 2,200 
volts and 25 cycles, used by the consumers in the immediate vicinity. 
A portion is, at the power-station by means of rotary converters, 
transformed to 500-volt direct current, and employed in operating 
the street railways. A third portion is, by means of static trans¬ 
formers, changed to a triphase current at 11,000 volts, and trans¬ 
mitted to Buffalo. The transmission-line is an aerial pole-line for 
about 26 miles to the city limits of Buffalo, and an underground con¬ 
duit line to the distributing station. The poles are white cedar, 
shaved and painted, set from 7 ' to 8 ' in the ground. They are from 
35 feet to 65 feet in length, depending upon the contour of the ground, 
and vary from 14" to 28" in diameter at the butt, and not less than 
8" at the top. Two cross-arms, placed on each pole, carry four cir¬ 
cuits of three wires each, one circuit being placed upon each side of 
each pole, upon each arm. While the plant is operating at 11,000 
volts, the line is designed for 22,000 volts. Each wire is 350,000 
circular mils secured in a groove on top of the insulator, which is 
specially designed of porcelain, and tested to 40,000 volts. Light¬ 
ning-guards are provided in the shape of a line of barbed-iron fence- 
wire strung upon the outside end of each cross-arm ; at every fifth 
pole a lightning-arrester is attached. The aerial line ends at the city 
limits of Buffalo ; and from thence the circuits are spliced into cables, 
extended in terra-cotta conduit. The conduit is composed of twelve 
3" tile ducts. Each cable is 350,000 circular mils, having rubber 
insulation, covered with rubber tape, and protected with a lead 
sheath. 

691. The Ogden, Salt Lake City (Utah), Transmission-Plant. — 
Water-power is obtained from the Ogden River, six or seven miles 
from Ogden. A dam furnishes a large storage reservoir, from which 


MISCELLANEOUS METHODS. 


523 


water is carried through a flume five miles, to the power-house. The 
effective head is 450 feet, and the capacity of the pipe about 10,000 
H. P. Knight water-wheels, of 1,200 H. P. each, are directly con¬ 
nected to General Electric generators, delivering current at 2,300 
volts and 60 cycles. The generators are triphase alternators of 750 
kilowatts each. Five are in operation, with provision for ten in the 
future. Step-up transformers raise the voltage to 11,100 volts, and 
deliver the current to the transmission-line, consisting of two circuits, 
each consisting of three No. 6 bare copper wires strung upon porce¬ 
lain insulators, extending thirty-six miles to Salt Lake City. The 
line is built of cedar poles from 30 ' to 70 ' in length, 9 " to 10 " tops. 
Two cross-arms are supplied, the upper one carrying two wires, one 
on each side of the pole, while the lower one carries four wires, two 
on each side of the pole. The insulator-pins are so placed that the 
three wires on each side of the pole form an equilateral triangle of 
two feet on each side, making one circuit. Ordinarily the line poten¬ 
tial at Ogden is 16,100 volts, and at Salt Lake City 13,800 volts, 
showing a line-loss of about fourteen per cent. At Salt Lake City 
step-down transformers reduce the pressure to 2,300 volts for the 
secondary network. 

As an experiment, the two circuits were connected up in such a 
manner as to transmit power from Ogden to Salt Lake and back to 
Ogden again. The transformers were arranged for a pressure of 
30,000 volts; and 1,000 H. P. was thus transmitted over 73 miles 
of circuit, with a loss of nine per cent in the lines and four per cent 
in the transformers. 

692. The Portland (Oregon) Transmission-Plant. —The station 
is designed for an ultimate capacity of 12,000 H. P., of which 4,000 
is now in use. The wheel-plant consists of Victor turbine wheels of 
500 H. P. each, to which 450-kilowatt General Electric triphase gen¬ 
erators are directly attached, that deliver current at 6,000 volts to 
the transmission-line. The circuit is a bare-wire pole-line extending 
12 miles from the power-station to Portland. The sub-station con¬ 
tains transformers which reduce the line pressure to 1,000 volts for 
delivery to the secondary four-wire system, also rotary transformers 
for delivering current at 500 volts to the street-railway system. 

693. The St. Anthony Falls (Minn.) Plant. — The power-plant 
utilizes the Falls of St. Anthony. The wheel-plant consists of ten 


524 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


turbine wheels, of 1,000 H. P. each. The electrical equipment con¬ 
sists of seven 700-kilowatt triphase alternators, furnishing current at 
3,450 volts, with a frequency of 34§, and three 750 direct-current 
generators, furnishing current at 600 volts. Three sub-stations are 
provided, two in Minneapolis and one in St. Paul. Sub-station No. 1 
is two miles from the power-house. Sub-station No. 2 is four miles. 
Sub-station No. 3 is ten miles. To Nos. 1 and 2, current is carried 
at the generator potential of 3,450 volts, on two triple-conductor lead 
cables. For sub-station No. 1, the cables are No. 000 B. & S. wire. 
For sub-station No. 2, the cables are No. 0000 B. & S. wire. All the 
cables are laid underground in conduits of cement-lined pipe. At 
the sub-stations, reducing transformers lower the pressure to 400 
volts, and deliver it to rotary converters for supplying 600-volt direct 
current to the railway system. For sub-station No. 3, step-up trans¬ 
formers at the power-house raise the potential to 12,000 volts. The 
high-potential line is composed of one No. 0 triple concentric lead- 
covered cable. At sub-station No. 3, step-down transformers and 
rotary converters are used. 

694. Long-Distance Transmission with Continuous Current. 

— The transmission plants so far described have all been operated 
by alternating currents. A Swiss installation has recently been put 
in operation, by means of which direct currents are utilized for trans¬ 
mission. The instance in question is that of some paper-mills near 
Soleure. As the power-plant was insufficient, it was decided to 
increase the plant by rendering available a waterfall situated some 
twenty miles away. To this end two direct current gramme machines 
of 5,000 volts each were arranged to operate in series. While the 
machines have been tested to 5,000 volts, they usually operate under 
a potential of 3,300 volts, making 6,600 volts in the line. The 
machines are of especially careful design and of unusually strong 
construction. They deliver to the line about 40 amperes, corre¬ 
sponding to an output of some 400 H. P. The line operates under a 
fall of potential of 600 volts. Bare copper conductors are used for 
the line construction, of seven millimeters diameter. The line is 
entirely aerial, and, passing through a mountainous country, is liable 
to injury from lightning. At the paper-mills two motors are 
used, similar to the generators in design and construction. The 
commercial efficiency of the plant, from the shaft of the turbine 



MISCELLANEOUS METHODS. 


525 


at the power-station, to the motor shaft, is said to exceed 75 per 
cent. 

695. Line Construction for Long-Distance Transmission. — 

While the greater preponderance of thought in designing for a long¬ 
distance transmission plant must be expended upon the station and 
design of the machinery therein, the circuit should by no means be 
omitted from consideration. To transmit energy at sufficiently high 
potentials to make long-distance transmission a commercial success, 
particular pains must be undertaken with the forms of insulation. 
On the whole, probably, a bare wire line carefully supported upon 
adequate poles presents the best solution. It may be argued that a 
pole-line is specially exposed, and is liable to destruction from the 
severity of the elements. It is certainly feasible to construct a line 
sufficiently strong, so that it shall be perfectly capable of withstand¬ 
ing all the present known exigencies of the elements, at least in 
temperate climates. This merely means sufficiently heavy and 
strong poles, placed near enough together so that the line loads, due 
either to wind stresses or to the accumulation of sleet and ice, may 
never be sufficient to break the line down, and is readily accomolished 
by the use of steel supporting poles, built short and strong. 

696. By placing the poles sufficiently near each other, the ten¬ 
sion of the spans can be reduced almost to any desired limit, that 
the conductors may never rupture from overloading. By further 
providing insulated cables, there would seem to be little probability 
that grave difficulties would arise from short-circuiting by the cross¬ 
ing of the conductors themselves. The difficulty of insulation at 
the poles, however, is a more serious one, some form of fluid insu¬ 
lator probably providing the best solution of the problem. While 
the adoption of the underground conduit, as indicated in the Niagara 
plant, affords complete protection from the elements, it seems a very 
open question as to whether it will be practicable to keep a conduit 
sufficiently dry to render the circuits safe, and also whether it will 
be possible for workmen to enter the conduit for purposes of repairs, 
when the plant is in operation. It is also quite certain that, should 
any accident occur in a section of conduit with the conductors in 
close proximity to each other, the resultant damage to the circuits 
would be incomparably greater. In addition to the mechanical 
features of line construction and insulation, presented in the long- 


526 THE ELECTRICAL TRANSMISSION OF ENERGY. 

distance transmission problem, there now arises for consideration the 
effects of impedance and capacity, when the line is used for the trans¬ 
mission of alternating currents of high frequency. 

Unfortunately, while the probable theoretical behavior of circuits 
under an alternating current can be fairly calculated, provided all of 
the constants are accurately known, the variables are so great in 
number, and there is as yet so limited experience in transmission of 
this kind, that the best and most careful mathematical calculations 
are liable to lead to unexpected results, chiefly owing to present 
inability to assign to all variables their proper values. This is 
notably the case when it is considered the practical impossibility of 
deducing the true form of the current wave in a dynamo that is yet 
only designed. Certain it is, from experiments already made in long¬ 
distance transmission, and especially with high frequencies, that the 
effect of capacity and impedance exercises a very marked effect upon 
line transmission and the ability to utilize the energy at the receiving- 
station. With each wave of current, the entire line must be filled 
and discharged ; so with high frequencies absorption of energy by 
the line will interfere materially with the efficiency of the plant, and, 
further, the line, by its capacity, may give rise to discharge currents 
at the receiving-station of enormous magnitude. It is probable, that 
in an endeavor to meet these difficulties, the designers of the Niagara 
plant have selected the low frequency of 16§ per second for their 
generators. It is their expectation that this frequency will be suffi¬ 
cient to produce insensible variation in ordinary illumination ; and at 
the receiving-station, in order to overcome the capacity effect, it is 

proposed to use an artificial load for the starting of the motors. 

697. Relative Amount of Conducting Material for Trans¬ 
mission S/stems. — In connection with the discussion upon the 
design of the Niagara transmission plant, the question of the 
relative amount of copper necessary to employ in a conducting sys¬ 
tem has been made the subject of extended investigations by Mr. 
Kennedy, Dr. Bell, Mr. Steinmetz, Mr. Kapp, and others. In con¬ 
sidering the relative amount of conducting material, it is necessary 
to observe that there are two aspects to the problem. In the case 
of alternating currents, the electro-motive force is constantly varying 
with the phase of the current ; and not only the amounts of ohmic 
resistance and impedance of the conductors are to be taken into con- 


MISC EL LA NEO US ME T/IODS. 527 

sideration, but the electrical stresses to which the insulating material 
is subjected must not be forgotten. With continuous currents 
electro-chemical effects also come into play. If the electro-motive 
force effective at the termini of the translating device be assumed, 
it is quite easy to show that the alternating systems are considerably 
more economical in conducting material than the direct current 
systems, and that the multiphase systems are still more economical 
than the diphase. This, however, leaves the important consideration 
out of the problem of the electrical stresses on the insulators. 
Nearly all investigators agree with the following results obtained by 
Mr. Kennedy and Mr. Steinmetz, as given in the Electrical World, 1 
and by Loppe et Bouquet. 2 

Table No. 55. 

Giving Relative Amounts of Conducting Material in Various Conducting Systems, 



On Basis of 
Equal Effective 
E.M.F. at 
Translating Device. 

On Basis of 
Maximum E.M.F. 
Between 
Conductors. 

Continuous current (metallic circuit) . . . 

100 

100 

Simple alternating current (metallic circuit) . 

100 

200 

Diphase with common return wire .... 

73 

291 

Triphase system Y connections. 

25 

150 

Triphase system L\ connections. 

75 

150 

Continuous current three-wire, allowing 60 



per cent of outside copper to neutral wire . 

32.5 

130. 

Five-wire continuous current system, allow- 



ing also 60 per cent of outside copper to 



inside wires. 

11.9 

190. 


1 Electrical World , vol. xxiii. p. 3 . 

2 Courants Alternatifs Induslriels , par Loppfe et Bouquet, p. 194 . 












528 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


CHAPTER XII. 

THE COST OF PRODUCTION AND DISTRIBUTION. 

698 . The problem of determining the cost, either of an installa¬ 
tion for the distribution of energy, or the price of producing that 
energy, is one containing so many factors, each of which are varia¬ 
bles within so wide limits, and are so modified and controlled by local 
circumstances, that a general solution is an impossibility. Yet to 
afford some assistance toward an approximate general solution under 
conditions - which are likely to be frequently realized, and to enable 
the designer to obtain figures necessary for the application of the 

Table No. 56 . 

Cost of Conductors. 
































































































THE COST OF PRODUCTION AND DISTRIBUTION 


529 




m 

u 

o 

+3 

o 

3 

73 

O 

O 


O 

M 

o 

O 


to 

*0 


d 

£ 

w 

j 

w 

< 

H 









































































































































530 TIIE ELECTRICAL TRANSMISSION OF ENERGY. 

economical formulae given in Chapters IX. and X., the following 
data are presented. 

699. Cost of Conductors. — In Chapter IX., it has been shown 


Table No. 56 ( Continued ). 

Cost of Conductors. 



that the cost of conducting mains may be expressed by an equation 
of the form of y — a-\-bx. 

In sheets A, B, C, D, E, and F, Table No. 56, are given the 




























































THE COST OF PRODUCTION AND DISTRIBUTION. 


531 


curves calculated by the foregoing equation, for a number of the 
more common electrical conductors. In determining these curves, 
the cost of copper has been estimated at seventeen cents per pound, 
and the cost of the various kinds of insulation determined from the 
manufacturer’s current price-list, without any attempt at the inclu- 

Table No. 56 ( Continued ). 

Cost of Conductors. 



sion of the various trade discounts, which are factors too uncertain 
to be embraced in tabular values of this kind. All of the curves are 
plotted with the axis of x as the function of conductor area in square 
inches, while the axis of y indicates the cost in dollars, per mile, 
for the corresponding areas. On sheet A will be found curves for 






















































































532 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


underwriters’ line wire, weather-proof wire, compound insulated wire, 
electric-light cables, and telephone cables. In the case of the first 
four curves, the copper areas are square inches of conductor section 
for the whole cable. In the case of the telephone cables, the copper 

Table No. 56 ( Continued ). 


Cost of Conductors. 



area is the sum of the areas of all of the conductors included in the 
cable, it being hardly necessary to state that the individual conduc¬ 
tors are insulated from each other, in order to render them applicable 
to telephone service. In sheets B and C, two other series of curves 































































































THE COST OF PRODUCTION AND DISTRIBUTION. 533 

are given. In sheets D, F, and G will be found some of the more 
prominent cables made by English manufacturers ; the prices, how¬ 
ever, correspond very closely to those of American make. 

700. Cost of Conduits. — In Chapter IX. it was also shown 


* 

1 able No. 56 (Continued ). 

Cost of Conductors. 



that the cost of conduit systems could be expressed by an equation 
similar to that of copper conductors, of the form, y = a + b'x. 

On sheets W, X, Y, and Z, T able No. 57, the curves for costs of the 
more prominent forms of conduit are given. On sheet X the cost 
of the Johnstone System is plotted, the axis of x being the duct 











































































































534 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


capacity in square inches, while the axis of y is the cost per mile in 
dollars. On sheet Y may be found similar curves for the cost of the 
Crompton System as built in London. 

On sheets W and Z the underground conduits more commonly used in 
this country, consisting of 10"xl0" terra-cotta pipe, 5" x 5" single¬ 
duct terra-cotta pipe, cement-lined pipe, and iron pipe, are indicated 
in a similar manner. In calculating the cost of conduit, the prices 
of ducts, per foot, are assumed as they would average at any one of 


Table No. 57. 


Cost of Conduit. 



the larger cities, either along the Atlantic Coast, or east of the 
Mississippi River. Prices of labor are estimated at $2.00 per day ; 
the cost of repaving for macadamized streets at 60 cents per square 
yard, wooden paved streets at $1.00 per square yard, and granite 
paved streets at $1.50 per square yard, 10 per cent allowance being 
made for waste and loss in paving materials. The manholes have 
been estimated at intervals of 300 ft., and are supposed to be 5 ft. 
wide, 7 ft. long, and 5 ft. in depth, with 8" common brick wails 
laid in hydraulic cement. The conduits have been estimated at an 







































THE COST OF PRODUCTION AND DISTRIBUTION 


535 


12000 


11000 


10000 


9000 


£ 8000 
cc 
< 

O 7000 

Q 

Z 

IlI 6000 


CC 
ll! 5000 

Q. 

h- 

CO 
O 


o 


4000 


3000 


2000 


1000 


Table No. 57 ( Continued ). 

Cost of Conduit. 






Y 





c 

ROM 

PTOh 

rs s> 

r- 

LlI 

H 

C 0 

__, 





u 

NDEF 

GRO 

r 

UND 

MAIN 

S. 




































• 


















































15’ 


3 way 
or 3 

DUCT CAPACITY. 


20 " 
fr » 

5 way 
6 


24" Culvert. 

- I 

7 way 

9 Pipes. 


average depth of 3 ft. below the surface of the ground, with no 
special allowance for the removal or replacement of complicated 


underground structures. 


701. Cost of Pole-Lines. — In Table No. 58, the average 
cost of the construction of pole-lines such as would be suitable, 































536 


THE ELECTRICAL TRANSMISSION OF ENERGY 


Table No. 57 ( Continued ). 

Cost of Conduit. 


41000 

40000 

39000 

38000 

37000 

36000 

35000 

34000 

33000 

32000 

31000 

c/5 30000 

CC 

< 29000 

_l 

-I 28000 

o 

Q 27000 
Hr 26000 

W 25000 

1 24000 

CC 23000 

LU 

0 - 22000 

^ 21000 


o 


20000 

19000 

18000 

17000 

16000 

15000 

14000 

13000 

12000 

11000 

10000 










7 





















IT 














u 

MC 

>E 

RGR 

O 

JIS 

ID 

C 

O 

NDU 

IT 

S 1 

































































& 




















a 

y 

.Si 

<b 


















T 






















9 




















/O 

r 








































































































4 

* J 










i 










..-y 
0/ 

y 












* 



















































































































































































i0' 



















1| 




































































































































28 35 42 49 56 63 70 77 84 91 98 105 112 119 126 133 140 147 154 161 168 175 sq.in. 

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Cables. 

DUCT CAPACITY. 


either in urban districts, or in an open country for ordinary aerial 
lines, or for common electric railway feeder lines, is given. The 
estimate is made up for various sizes of poles, from 30 to 50 ft. 
inclusive, per mile of poles, without arms. In addition, the cost 




















































































THE COST OF PRODUCTION AND DISTRIBUTION. 


537 


of cross-arms complete with insulators, and the cost of stringing 
bare wire, not over No. 8 gauge, either iron or copper, is indicated. 
From the figures here given, it is reasonable to assume that an 
average estimate of the cost of line construction may be made when 
the number of wires to be strung is determined upon. 

702. Railway Lines.—The cost of building electrical railway 
lines may be divided into two parts, the cost of the trolley line 
proper, and the cost for the necessary feeds, and the erection of the 
same. A trolley line for a double-track road with wooden poles, using 


Table No. 58. 

Cost of Pole Lines. 

Cost per mile of Line Poles set, but without arms. 

Cost of one ten -pin arm, complete with insulators on pole, $1.30, common. 
Cost of one ten-p\n arm, complete with insulators on pole, $1.90, yellow pine. 
Cost of stringing wire per mile, $2.50 to $10.00. 

The cost of “ Anchor Poles ” is the cost for each pole complete. 


Location. 

Height of Poles. 

30 Ft. 

40 Ft. 

45 Ft. 

50 Ft. 

Line.— 

Anchor. 

Line. 

Anchor. 

Line. 

Anchor. 

Line. 

Anchor. 

City Line, Favorable Circumstances . . 
City Line, Unfavorable Circumstances . . 

Country Line, Favorable Circumstances . 
Country Line, Unfavorable Circumstances 

$500 

550 

250 

300 

$135 

160 

$675 

725 

400 

450 

$150 

180 

$800 

875 

500 

575 

$160 

190 

$1050 

1200 

775 

900 

$175 

200 


one of the cheaper style brackets, may be built for from $800.00 to 
$1,200.00 per mile. If iron poles are used, the cost will be from 
$1,200.00 to $1,600.00 per mile. These figures presuppose center- 
pole construction. If side-pole construction is used, the cost for 
wooden poles will be increased by about $200.00 per mile, while the 
cost for iron poles will be augmented by from $400.00 to $600.00 per 
mile. The cost for stringing feed-wires, including insulators, pins, 
arms, etc., will vary from $50.00 to $100.00 per mile, depending upon 
the number of feeds and the size of the wire. For a complete elec¬ 
trical railway line, the following figures, obtained from some twenty 
representative roads in this country, will serve as a fair average. 


























538 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


Table No. 59. - Cost of Street Railway Lines. 

COST PER MILE. 

Round wooden poles, unpainted.$2,000.00 to $2,500.00 

Machined wooden poles, painted and set in soft 

soil. 2,500.00 to 3,000.00 

Iron poles, center construction. 4,000.00 to 5,000.00 

Iron poles, span-wire construction. 5,000.00 to 6,000.00 

The above figures include the cost of the feeds ; but on most of 
these roads the amount of copper was smaller than the requirements 
should justify, so that, properly speaking, these figures should be 
increased by some 10 to 15 per cent, in order to afford a sufficient 
amount of copper for adequate service. A detailed estimate of the 
cost of overhead line work will be found in Table No. 60. 

703. Street Railway Operating Expenses. — The cost of oper¬ 
ating an electrical railway depends, as is the case in every electrical 
plant, on the size, the daily hours of service, and care and skill exer¬ 
cised in administration. In Table No. 61 will be found the “ Mile¬ 
age,” “Cost of Power,” “Cost of Repairs,” and “Cost of Removing 
Snow ” for nineteen representative roads, from which a close estimate 
of probable actual operating costs can be obtained. 

Table No. 61. 


Operating Expenses of Street Railways. 


Name. 

Mileage. 

Cost of 
Electric 

Power. 

Cost of Re- 
pairs to 
Wiring, etc. 

Cost Re¬ 
moving Ice 
and Snow. 

Per Car Mile. 

Per Car Mile. 

Per Car Mile. 

Brockton . 

883.254 

$0.0203 

$0.0027 

$0.0039 

Fitchburg and Leominster .... 

323.436 

.0248 

.0017 

.0056 

Globe (Fall River). 

729.378 

.0206 

.0009 

.0039 

Gloucester . 

214.658 

.0400 

.0009 

.0034 

Haverhill and Amesbury. 

413.560 

.0443 

• • • 

.0033 

Holyoke. 

266.688 

.0350 

.0006 

.0084 

Interstate. 

331.563 

.0596 

.0010 

.0037 

Lowell, Lawrence, and Haverhill . . 

305.694 

.0396 

.0007 

• • • 

Lowell and Suburban. 

1,276.257 

.0137 

.0001 

.0063 

Lynn and Boston. 

4,059.479 

.0223 

.0015 

.0070 

Merrimack Valley. 

303.933 

.0410 

.0023 

.0112 

Newburyport and Amesbury . . . 

258.191 

.0294 

.0042 

.0104 

Newton. 

265.503 

.0360 

.0036 

.0050 

Quincy and Boston. 

151.909 

.0573 

.0023 

.0090 

Springfield. 

1,441.768 

.0301 

.0026 

.0090 

Union. 

580.482 

.0077 

.0000 

.0020 

West End. 

18,669.809 

.0235 

.0053 

.0055 

Worcester. 

1,208.854 

.0100 

.0005 

.0044 

Worcester, Leicester, and Spencer . 

351.851 

.0389 

.0056 

.0095 
































THE COST OF PRODUCTION AND DISTRIBUTION. 


539 


o' 

CO 

o' 

£ 

w 

CQ 

< 

H 
























































540 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


704. Cost of Power-Stations. — The cost of power-stations, ex¬ 
cluding the expense for real estate and buildings, varies greatly' with 
the type of prime mover employed, and with the conditions necessary 
to obtain good foundations, and with other local circumstances. 
The following figures are fair averages. 

TABLE No. 62. - Cost of Power-Stations. 

High-speed simple engines.SI().()() to $15.00 per H. P. 

High-speed compound engines .... 12.00 to 20.00 per H. P. 

Condensing engines.15.00 to 25.00 per H. P. 

Triple-expansion engines. 20.00 to 30.00 per H. P. 

Boilers, horizontal iron tubular .... 9.00 to 12.00 per H. P. 

Boilers, vertical iron tubular.11.00 to 14.00 per H. P. 

Boilers, water-tube safety. 15.00 to 25.00 per H. P. 

Dynamos. 20.00 to 30.00 per H. P. 

Sundries. 10.00 to 20.00 per H. P. 

Averages taken from the best stations throughout the country, 
capable of supplying from 500 to 1,000 H. P., will show a total 
expense for machinery and installation of from $55.00 to $80.00 per 
horse-power of station. 

705. The Cost of Producing Energy. — The cost of produ 
cing energy in the various stations throughout the country varies 
greatly with the price of labor and the cost of fuel. The most 
accurate information upon this subject has been calculated and 
compiled by Dr. C. E. Emery, and presented to Electrical Engi¬ 
neers in the Transactions of April, 1893. In this paper Dr. Emery 
summarizes all of the cost entering into production and mainte¬ 
nance of power for engines which are reasonably well loaded, and 
for stations of medium capacity, say 500 H. P. Taking Dr. Emery’s 
figures as a basis, Table No. 63 has been calculated, showing the 
cost of delivering electrical energy at the terminals of the genera¬ 
tors in the supply station. Two sets of values are here given, 
one for 3,080 kilowatt hours per annum, equivalent to the operation 
of the station for 308 days of ten hours each ; the other is the cost 
of the production of 7,300 kilowatt hours per annum, or equivalent 
to the operation of the station for 365 days of 20 hours each. In 
this latter table such a sufficient margin in capitalization is intro¬ 
duced as will provide for about 50 per cent extra machinery to meet 













THE COST OF PRODUCTION AND D IS TRIP UTIOA T . 


541 


cases of break-downs, and to provide for special station loads. In 
the lower part of this table these costs have been further computed, 
showing, under each circumstance, and for each of the varying fuel 
prices, the cost of the production of one kilowatt hour. 


Table No. 63. 

Cost of Producing Electrical Energy per Kilowatt for 308 Days of 10 Hours, 

and 365 Days of 20 Hours. 



Type of Engine. 

OF 

308 DAYS 

10 HOURS EACH. 

OF 

365 DAYS 

20 HOURS EACH. 


Cost 

of Coal 

per 2240 lbs. 

Cost 

of Coal 

per 2240 lbs. 



$ 2.00 

$3.00 

$4.00 

$5.00 

$ 2.00 

$3.00 

$4.00 

$5.00 

1 

r Simple High Speed . . 

$55.80 

$65.28 

$74.78 

$84.25 

$95.55 

$117.00 

$138.43 

$159.90 

§ s] 

2 -8 
c 

Compound High Speed 

49.33 

55.80 

65.23 

71.74 

82.72 

99.61 

116.52 

133.44 

o 

^ Simple Low Speed . . 

57.46 

62.99 

71.55 

89.01 

90.35 

109.70 

129.01 

148.36 


r Simple High Speed . . 

44.85 

51.14 

57.46 

63.79 

75.57 

88.86 

103.16 

117.45 

bio 

c 

in 

■ c 

Compound High Speed 

43.93 

49.68 

55.41 

61.16 

71.88 

84.87 

97.88 

110.87 

V ' 

c 

o 

Simple Low Speed . . 

44.88 

50.77 

56.67 

62.58 

72.40 

86.40 

99.07 

112.40 


^ Compound Low Speed 

43.75 

49.06 

54.36 

59.64 

69.43 

81.44 

93.44 

105.34 



Cost 

per Kilowatt 

Hour. 





hi) 

c 

r Simple High Speed . . 

1.8117 

2.119 

2.428 

2.7355 

1.3089 

1.6028 

1.8963 

2.1905 

Non- 

indensi 

Compound High Speed 

1.6015 

1.8117 

2.118 

2.3294 

1.1335 

1.3647 

1.5962 

1.8278 

U 

u 

^ Simple Low Speed . . 

1.8655 

2.0450 

2.323 

2.890 

1.2375 

1.503 

1.7685 

2.0322 


( Simple High Speed . . 

1.4560 

1.6603 

1.8655 

2.071 

1.0353 

1.2172 

1.4192 

1.600 

ti 

C 
i n 
c 

Compound High Speed 

1.4262 

1.6130 

1.7993 

1.9858 

0.9847 

1.1628 

1.341 

1.519 

V 1 
T3 

C 

o 

Simple Low Speed . . 

1.4570 

1.6475 

1.8400 

2.032 

0.9918 

1.1836 

1.357 

1.5398 

O 

^ Compound Low Speed 

1.4203 

1.5928 

1.7619 

1.9364 

0.9514 

1.1156 

1.2800 

1.444 


706. Coal-Consumption per Watt Hour. — From a report 
made to the National Electric Light Association, Feb. 29, 1894, 
by a committee specially appointed to investigate the subject, 
the data exhibited in Table No. 64 are obtained as indicating the 
actual consumption of coal in plants in commercial service per 


















































542 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


watt hour produced. The table indicates an average yield of 92 
watt hours per pound of coal consumed. The advantage of large 
units and continuous operation is exhibited in the case of the de¬ 
livery of 208 watt hours per pound of hard screenings in a plant 
loaded to 4,000,000 watts running 24 hours per day, as contrasted 
with 30 watt hours per pound of soft coal, with an output of 60,000 
watts and a seven-hour service. Assuming a mechanical efficiency 


Table No. 64. 


Actual Watt Hours Delivered Per Pound of Coal—Commercial Plants. 


1 

2 

3 

4 

1 

2 

3 

4 

Hours 
per day 

Watt Hours 


Watt 
Hours 
per lb. 
of Coal. 

Hours 
per day 

Watt Hours 


Watt 

H ours 

of Oper- 

per day 

Kind of Coal. 

of Oper- 

per Day 

Kind of Coal. 

per lb. 
of Coai. 

ation of 
Plant. 

Delivered. 


ation of 
Plant. 

Delivered. 


24 

1,009,070 

Slack 

150 

6 

91,368 

Lehigh Pea 

65 

15| 

187,860 


04 

14* 

377,000 

Buckwheat 

90 

6 

312,000 


72 

15 

990,000 

Ant. Buckwheat 

110 

6 

361,800 

Slack 

45 

12 

336,000 

Pardee Soft 

96 

9 2 l 

2,090,000 

Indiana Block 

53 

16 

787,520 

Bituminous 

121 

24 

259,000 

Indiana Block 

166 

15 

1,248,000 

Buckwheat 

192 

7 

59,500 

Soft 

30 

24 

1,002,624 

Pittsburgh 

122 

10 

247,500 

Slack 

56 

14 

312,666 

Leh. Valley Pea 

109 

14* 

381,023 

Soft 

52 

n 

267,375 

Bituminous 

76 

6 

110,880 

Pea 

110 

16.3 

547,028 

Buckwheat 

114 

15 

270,000 

Slack 

46 

24 

3,750,000 

Soft Coal 

68 

6 

279,000 


70 

10 

246,000 

Coal 

117 

8 

152,000 

Slack 

108 

10 

246,001 

Lump 

46 

24 

12,920,136 

Screenings 

183 

5 

72,800 

Slack 

40 

24 

2,217,600 


• 

9 

135,000 

Bituminous 

56 

24 

3,840,000 

Hard Screenings 

208 

11 

242,000 

McAl. Lump 

76 

18 

586,740 

Soft 

186 

7J 

171,197 

Iowa Slack 

47 


of 90 per cent in the transmission from the engines, and the same 
figure for the conversion in the dynamo, a yield in watt hours per 
pound of coal as indicated in Table No. 65 should be obtained. 

707. Water-Power. — The value of electricity as a means of 
distributing energy has been especially extolled in connection with 
the utilization of water-powers. In many cases the claims made for 
this means of distribution have been fully substantiated. It should, 
however, be recollected that, in most cases where available water- 
powers exist in proximity to centers where there is a demand for 
power, the water-powers have been already made thoroughly avail- 






























THE COST OF PRODUCTION AND DISTRIBUTION 


543 


able, as, for example, in many of the rivers upon the Atlantic Coast, 
especially in the North-eastern States. In the far West, where 
water-powers are more plenty, settlement is, as yet, so sparsely 
distributed that, even were all the machinery for availability in 
place, the power could not be sold for lack of customers. Some 
special cases will, however, undoubtedly from time to time appear, 
as for example, in the present undertaking to utilize a portion of 
the water-power of the Niagara, and transmit the same to the neigh¬ 
boring cities, in which the availability of electricity will prove itself 
of exceeding value. Dr. Emery has shown, by careful computation, 
that in many cases the cost of improvement required for the utiliza¬ 
tion of water-power reaches a sum so large that the interest and 
depreciation upon the same, in the end, aggregate more than the cost 

Table No. 65. 


Possible Watt Hours Per Pounds of Coal. 


Coal Consump¬ 
tion per I. H. P. 

in Pounds. 

Possible Watt 
Hours Pro¬ 
duced. 

Coal Consump¬ 
tion per I. H. P. 
in Pounds. 

Possible Watt 
Hours Pro¬ 
duced. 

1.5 

402 

5 

120 

2 

302 

6 

100 

3 

201 

7 

86 

4 

151 

8 

75 


of power production by means of steam ; and that it is only under 
very exceptional circumstances that a cost of more than $140.00 per 
H. P. obtained is justified as an improvement expense. 

708 . So far as station equipment expenses are concerned, it is 
found that the cost of water-wheels, penstocks, shafting, etc., re¬ 
quired to deliver the power to the dynamo, is very nearly as great as 
that incurred in steam machinery. A fair average, perhaps, may be 
taken at from $40.00 to $75.00 per horse-power rendered available. 
The actual cost of water-power throughout this country is quite 
an uncertain quantity. In the New England States, the cost 
averages nearly $20.00 per horse-power per year, thus approximat¬ 
ing to the cost of steam-power. 

709 . In some of the Southern States, where water-powers are 
less fully in demand, the cost is lower, varying from $12.00 to 
$15.00 per annum per horse-power. So, while electricity lends 













544 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


itself most readily to the transmission of power over comparatively 
long distances, the financial outcome of the utilization of any water¬ 
power should be closely scrutinized, both from the standpoint of 
the probable expense of the necessary improvement required, and 
also from the standpoint of the ability to find customers for the 
power obtained when the development shall be complete. 

710. The Gas-Engine. — Internal conbustion engines, or gas- 
engines as they are more frequently called, are deserving of notice 
as prime movers for electrical plants under some circumstances. 
As the gas-engine requires no boiler, the apparatus requires less 
space for installation than is necessary in the case of steam. Very 
much less care and attention are needed to operate the engine, as 
there is no fire to tend, and no steam pressure to watch. As there 
is no possibility of an explosion, a licensed engineer is not, by city 
regulations, required as an attendant, and a much cheaper grade of 
labor may be employed. Per contra, fuel in the form of gas is, 
except in specially favored locations, much more expensive per unit of 
output than coal, notwithstanding the greater engine efficiency. The 
engine itself is much more complicated, and entails a greater cost 
for maintenance. 

711. With a good quality of gas supplied at a fair and steady 
pressure, the consumption of gas per brake horse-power varies greatly 
with the size of the engine. Average values of gas required will be 
found in Table No. 66. 

TABLE No. 6b.-Cubic Feet of Gas per Hour per B. H. P. Output. 

Brake horse-power .... 3 5 10 15 20 25 50 75 100 

Cubic feet of gas used per hour, 37 32.5 28 25 23 21.5 19 17 16 

712. The cost of engine and installation will vary from $50.00 
per horse-power for small sizes to $35.00 for the larger ones. With 
gas at $1.00 per M. the cost of producing electrical energy may be es¬ 
timated at 7 to 10 cents per K. W. hour for small engines under ten 
horse-power, and from 3 to 5 cents far engines of fifty horse-power 
and over. As these figures are from one-half to two-thirds of the 
cost of operating small steam-engines, the economy of the gas-engine 
for very small plants is evident. With large installation the steam- 
engine is usually considered to show a much greater economy than 


THE COST OF PRODUCTION AND DISTRIBUTION. 


545 


Table No. 67. 

Showing Cost of Electric Lighting by Wind-Power. 


Diameter of Wind-wheel in Feet. 

Cost of Geared Windmill, Shafting, and 
Tower. 

— 

Useful Horse-Power Developed, Wind 
16 Miles per Hour. 


Expense of Power 
Cents per Hour. 


Watts Recovered from Dynamo, 50 per 
cent Efficiency. 

Cost of Dynamo. 

Expense of Gen¬ 
erating 
Electricity. 

Watt Hours Recovered from Accumu¬ 

lators per Day, Efficiency 45 per cent. 

Av. No. of Hours this H.-P. 
will be Developed per Day. 

Interest on First Cost at 5 per 
cent per annum. 

Depreciation at 5 per cent. 

Attendance. 

o 

Interest on First Cost. 

Depreciation at 5 per cent. 

O 

8* 

$153 

0.64 

8 

0.26 

0.26 

0.06 

0.04 

14.9 

$15 

$0.03 

$0.03 

$0.05 

53.7 

10 

164 

0.12 

8 

0.28 

0.28 

0.06 

o.w 

44.8 

20 

0.03 

0.03 

0.05 

161.1 

12 

177 

0.21 

8 

0.30 

0.30 

0.06 

0.04 

78.3 

25 

0.04 

0.04 

0.06 

279.6 

13 

181 

0.25 

8 

0.31 

0.31 

0.06 

0.07 

93.2 

30 

0.05 

0.05 

0.06 

335.7 

14 

227 

0.28 

8 

0.39 

0.39 

0.06 

0.07 

104.4 

35 

0.05 

0.05 

0.06 

376.0 

16 

301 

0.41 

8 

0.51 

0.51 

0.06 

0.07 

152.9 

40 

0.07 

0.07 

0.10 

550.5 

18 

350 

0.61 

8 

0.60 

0.60 

0.06 

0.07 

227.5 

50 

0.08 

0.08 

0.10 

1,433.4 

20 

373 

0.79 

8 

0.64 

0.64 

0.06 

0.10 

279.7 

60 

0.10 

0.10 

0.30 

1,761.9 

22 

544 

1.23 

8 

0.93 

0.93 

0.06 

0.10 

458.8 

130 

0.22 

0.22 

0.30 

2,890.4 

25 

584 

1.34 

8 

1.00 

1.00 

0.06 

0.10 

499.8 

140 

0.24 

0.24 

0.40 

3,148.9 

30 

679 

2.40 

8 

1.16 

1.16 

0.06 

0.13 

895.2 

175 

0.30 

0.30 

0.40 

5,639.8 

36 

743 

2.95 

8 

1.27 

1.27 

0.06 

0.13 

1,100.3 

210 

0.36 

0.36 

0.50 

6,932.2 

40 

842 

4.42 

8 

1.44 

1.44 

0.06 

0.13 

1,648.7 

270 

0.46 

0.46 

0.50 

10,386.6 

50 

1,592 

6.88 

8 

2.73 

2.73 

0.06 

0.16 

2,566.2 

300 

0.51 

0.51 

0.60 

16,167.3 

60 

1,902 

10.00 

8 

3.26 

3.26 

0.06 

0.16 

3,730.0 

400 

0.68 

0.68 

0.80 

23,499.0 


• H 

"3 

Number of Lamps 16 C. P. 
110 Volts. 

Number of Hours Lamps 
will run per Day. 

1 • 

3 c n 
u ir 

y o 

U 

O 

>a 

U 

V 

+-» 

Expense of Storing 
the Electricity. 

bJO 

C 

C/5 

U 

3 

O 

U-i 

O 

Average Cost of Lamp-Hour 
from Wiod-Powerin Cents. 

Diameter of Wind-whe 
Feet. 

Required Capacity of A 
mulatorsin Ampere H< 

Cost of 58 Accumu 
Cells. 

Cost of Automatic Ba 
Regulator. 

Interest on First Cost. 

Depreciation at 20 
per cent. 

Attendance. 

Total Expense of Obta 
Electricity per Hour 

Total Cost of the 8 H 
Daily Storage. 

Equivalent Number 
Lamp-Hours. 

8* 

1 

0.84 

4 

$21 

$20.00 

$0.07 

$0.28 

$0.24 

$1.32 

$10.56 

0.S4 

12.57 

10 

1 

2.52 

4 

21 

20.00 

0.07 

0.28 

0.24 

1.36 

10.88 

2.52 

4.32 

12 

1 

4.38 

5 

27 

20.00 

0.08 

0.32 

0.24 

1.48 

11.84 

4.38 

2.70 

13 

1 

5.26 

6 

32 

20.00 

0.09 

0.36 

0.24 

1.60 

12.80 

5.26 

2.43 

14 

1 

5.89 

7 

37 

20.00 

0.10 

0.40 

0.24 

1.81 

14.48 

5.89 

2.46 

16 

2 

4.31 

10 

54 

20.00 

0.12 

0.48 

0.24 

2.23 

17.84 

8.62 

2.08 

18 

5 

4.49 

26 

124 

20.00 

0.25 

1.00 

0.24 

3.08 

24.64 

22.45 

1.10 

20 

6 

4.60 

32 

153 

20.00 

0.30 

1.20 

0.24 

3.68 

29.44 

27.60 

1.07 

22 

10 

4.53 

52 

249 

20.00 

0.46 

1.84 

0.24 

5.30 

42.40 

45.30 

0.94 

25 

12 

4.11 

57 

273 

20.00 

0.50 

2.00 

0.24 

5.78 

46.24 

49.32 

0.94 

30 

20 

4.42 

103 

470 

20.00 

0.84 

3.36 

0.24 

7.95 

63.60 

88.40 

0.72 

36 

25 

4.34 

125 

571 

20.00 

1.01 

4.04 

0.24 

9.24 

73.92 

108.50 

0.68 

40 

38 

4.30 

190 

868 

20.00 

1.52 

6.08 

0.24 

12.23 

98.64 

163.40 

O.CO 

50 

60 

4.22 

294 

1,278 

20.00 

2.22 

8.88 

0.24 

18.64 

149.10 

253.20 

0.59 

60 

85 

4.33 

427 

1,857 

20.00 

3.21 

12.84 

0.24 

25.19 

201.50 

368.00 

0.55 



































































546 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


the gas-engine, though under special circumstances, when either nat¬ 
ural gas or producer gas can be obtained at very low rates, the cost 
of power delivered by the gas-engine will compare favorably with that 
obtained from steam. In Europe the gas-engine is being tried to a 
much greater extent than in this country. Several of the large Con¬ 
tinental stations are operating solely in this way, and recently some 
English stations have be eneqnipped with 350 H. P. gas-engines. 

Table No. 68. 

Cost of Producing Electrical Energy per K.W. Hour. 



Cost in 

Cents of 

Location of Station. 

System. 

Fuel. 

Stores 

AND 

W atek. 

Labor. 

Total. 

N ewcastle . 

Steam Turbine. 

1.60 

.54 

1.76 

3.90 

Leeds . 

Alternating Current, Rope driving 

2.46 

.42 

2.74 

5.62 

Bournemouth. 

Alternating Current, Rope driving 

3.62 

.54 

2.48 

6.64 

House to House Company 

Alternating Current, Rope driving 

3.86 

.82 

2.50 

7.18 

Newcastle on Tyne . . . 

Alternating Current, Rope driving 

1.24 

.32 

1.44 

3.00 

Metropolitan Company . . 

Mixed System. 

3.60 

.48 

1.50 

5.58 

Eastbourne. 

Alternating Current, Rope driving 

2.84 

.28 

2.80 

5.92 

Exeter. 

Alternating Current, Rope driving 

2.70 

• 

• 

• 

City of London Company . 

Mixed System . 

2.48 

.46 

1.82 

4.76 

Chelmsford . 

Mixed System. 

1.92 

.32 

1.88 

4.12 

Chelsea . 

Motor Transformer. 

2.22 

.68 

1.54 

4.44 

Oxford. 

Motor Transformer. 

1.40 

.09 

2.48 

3.97 

Preston. 

Direct Current. 

3.30 

.90 

2.70 

6.90 

Liverpool . 

Direct Current . 

1.90 

.30 

.74 

2.94 

Birmingham. 

Direct Current. 

1.76 

.34 

1.64 

3.74 

Charing Cross. 

Direct Current. 

2.26 

.37 

1.22 

3.85 

Hare. 

Direct Current. 

2.52 

.40 

2.88 

5.80 

St. James. 

Direct Current. 

1.74 

.27 

1.38 

3.39 

Bradford. 

Direct Current. 

1.32 

.19 

1.62 

3.13 

Brighton. 

Direct Current. 

1.80 

.33 

1.72 

3.85 

Kingston. 

Direct Current. 

1.74 

.30 

1.22 

3.26 

Westminster. 

Direct Current. 

1.56 

.38 

1.90 

3.84 

Knightbridge. 

Direct Current. 

1.26 

.34 

1.20 

2.80 

Ideal Station. 

Direct Current. 

.54 

.06 

.40 

1.00 


Statistics are not yet to be obtained as to the economic performance 
of these large units, though the designers, with good foundation, 
predict favorable results. 

713. The Cost of Electrical Energy as Developed by Wind- 
Power. — In some localities, notably in the Western portion of this 
country, where fuel is high priced, it is feasible to utilize wind-power 
by means of windmills for the purpose of generating electricity. 





















































THE COST OF PRODUCTION AND DISTRIBUTION 


547 


Mr. G. H. Morse 1 has compiled some valuable statistics regarding the 
cost of developing power in this way, which are abstracted in Table 
No. 67. Owing to the uncertainty of the wind, it is necessary to 
provide a very large margin in the battery plant, or in times of calm 
weather there will not be a sufficient reserve. 

714. The Actual Cost of Electrical Energy. — Whether for 
the design of a new plant, or as a guide in the operation of an exist¬ 
ing installation, data as to present operating costs of representative 
electrical plants are of the utmost value to the engineer. A collec¬ 
tion of the best existing information has been made of practice both 
in this country and Europe, and will be found in Tables Nos. 68 
to 73 inclusive. 

Table No. 68 is given by Mr. Crompton, 2 and contains the actual 


Table No. 69. 


Cost of Producing Electrical Energy per Kilowatt Hour. 


Bradford Station. 

Cost in 1890 . 

1891. 

1893 . 


Liverpool Station. 

Cost in 1891. 

1893 . 


St. Pancras Station. 

Cost in 1892 . 

1893 . 


Westminster Station. 

Cost in 1891. 

1893 . 


Brighton Station. 

Cost in 1892 . 

1893 . 


Notting Hill Station. 

Cost in 1891. 

1893 . 



cost of producing electricity in twenty-three of the best English 
plants. The costs are itemized into “ Fuel,” “ Stores,” and “ Labor,” 
thus giving a very complete sub-division of the subject. For an 
ideal station, yet one within the limits of present engineering skill, 
Mr. Crompton estimates a capital of $2,500,000 to be required for an 
output of 5,000,000 K. IV per annum, and that it is possible to bring 
the cost of production only to about 1 cent per K. IV. hour. In this 
table there are no allowances for interest, depreciation, taxes, and 
management ; allowing l£- cents for these items, and \ cent for profit, 
it is calculated that, under the favorable conditions of a very large 
plant continuously operated, electricity could be sold at a profit at 


1 See Year Book Soc. Eng., University of Minnesota, 1894. 

2 See Journal Institute Electrical Engineers, June, 1894. 

















548 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


















































THE COST OF PRODUCTION AND DISTRIBUTION 


549 


3 cents per A. IV. hour. Present practice indicates that on the 
average the selling price must be about double this figure. 

715. There is no doubt that improved machinery, better engi¬ 
neering, and a more thorough study of electrical science, are constantly 
tending to reduce the cost of production. This is exemplified in 
Table No. 69, collected from data given by Mr. Stevens. 1 Here a 
comparison is given between the cost of production at six of the 
large English stations for the past three years. On an average, 
there has been a decrease of about 30 per cent in actual cost. From 
these figures it seems not impossible that Mr. Crompton’s expecta¬ 
tions may be realized. 

716. In the Electro-techmsche Zeitschrift , Max Meyer 1 gives an 
article on the operating expenses of a number of the largest stations 
on the Continent, from which Table No. TO is epitomized. The 
costs here are in the neighborhood of 5 cents per K. IV. hour. In 
Table No. 71 is a comparison of operating expenses of a large num¬ 
ber of central stations made by H. A. Foster. 2 As the data are 
derived from fifty-four plants, the averages would seem to be exceed¬ 
ingly trustworthy. The cost of production from these figures is seen 
to be about 5.4 cents per K. IV hour. In the same article, Mr. Fos¬ 
ter has made a very extensive collection of data from information 
obtained from a hundred and fifty lighting-stations in this country. 
As the range of the inquiries is very broad, Table No. 72 has been 
compiled from this source, embracing the figures thus obtained from 
actual practice as to the cost of installation and operation of lighting- 
plants. The cost of plant per K. IV includes buildings and real 
estate, whenever owned by the operating company, and also the cost 
of the circuits. On the whole, the costs per K. IV hour are higher 
than those from European stations, but it must be remembered that 
the foreign data are taken from very large plants under continued 
operation. To select from Table No. 72 stations of similar size will 
show a close agreement in operating costs. 

717. In the Review of Reviews , February, 1893, Mr. R. J. Fin¬ 
ley discusses “ American Street Fighting,” giving considerable data 
regarding the cost of plant and operation of municipal stations, in 
contrast with those of private ownership. The motive-power is not 
stated, an omission greatly detracting from the value of any compari- 

1 See Electrical World , vol. xxiv., p. 206. 2 Electrical Engineer , vol. xviii, p. 188. 


550 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


sons that may be instituted. A summary of the data is to be found 
in Table No. 73. All the figures apply to the operation of nominal 
2,000 c.p. arc lamps. 

718. Commercial Consideration of Transmission Problems. — 

Every long-distance installation, from a constructive standpoint, must 
be regarded as made up of three factors. 

First. A generating-station, including prime movers for utiliz¬ 
ing the source of energy, and dynamo machinery for transforming 


Table No. 71. 


Comparison of Operating Expenses of Central Station. 



Labor. 

Fuel. 

Supplies and 
Office. 

Total Cost 
in Dollars. 

Nature of Station. 

Cost per 
K.W. in 
Dollars. 

Per 

Cent of 
Total. 

Cost per 
K.W. in 
Dollars. 

Per 

Cent of 
Total. 

Cost per 
K.W. in 
Dollars. 

Per 

Cent of 
Total. 

Per K.W. 
Hour. 

14 American Municipal Sta¬ 
tions, Contin. Cur. Arc. . 

.0251 

42.9 

.0173 

29.6 

.0161 

27.5 

.0585 

5 American Municipal Sta¬ 
tions, Incandescent . . 

.0244 

40.9 

.022G 

37.9 

.0126 

21.2 

.0596 

1 American Municipal Sta¬ 
tion, Arc. New. . . . 

.0317 

54.2 

.0199 

34 

.0069 

11.8 

.0585 

G American Stations, Mixed 
Output of 5,300,000 K. W. 



.0095 

20 

. . . 

. . . 

.0473 

5 German Stations, Output 
1,907,900 K.W. . . . 

.0218 

4G.5 





.0469 

23 English Stations, avge. 
Crompton. 

.0144 

25.7 

.0222 

39.G 

.0194 

34.7 

.0560 

Ideal English Station, 
Crompton. 

.004 

15 

.0054 

20 

.0170 

65 

.0264 

Lowest Items in 23 Sta¬ 
tions, Weaver .... 

.0074 

19.8 

.0126 

33.8 

.0173 

46.4 

.0373 


mechanical energy into electrical energy at proper potentials for 
economical transmission. 

Second. The necessary line for transferring this energy from the 
generating-station to the receiving-station. 

Third. The receiving-station, embracing such dynamo machinery 
as is necessary to reduce the high potentials used in the line to con¬ 
venient voltage for distribution and use by customers. 

The vital consideration in all such installations then becomes the 
cost of energy delivered at the receiving-station by the transmission 










































THE COST OE PRODUCTION AND DISTRIBUTION 


551 


TABLE No. 72. -Cost and Operating Expenses of Lighting-3taticns. 



V+_| C 





Operating Expenses. 

C/D • 

<D 



c— to 

Total Firs 
Cost of Plat 
per K. IV. 
Capacity. 

be « ^ • £ 

tn L. ^ 
TJ <U £ 

<u be, • £ 

to\* £ 





a 

c n K 

Location of 

s * 11 


C S 3 

Gp c 

Labor 

per K. IV. 
Output. 

U 

V) S* . 



O ^ —• 

Plant. 

o y b s 

h g.g.2 

UQ^ 

Open 

Expe 

per A 

per Ar 

.2 

U o> £ 

Total 

per A 

per An 

Fuel pe 
A '.IV. 
Output 

Supplie 

per K. U 

Output 

Office pe 

K. IV. 

Output 

Fixed C 

r>er K. 

Total ( 

Total 

per A 
Out 

Arkansas. 









$ 

$ 

$. 

Hope. 

21.00 

$228.60 

$ 32.38 

$ 30.85 

$ 63.23 

$.0274 

$.0114 

. . 

.0371 

.0758 

Little Rock . . 
California. 

G9.G0 

570.97 

130.04 

77.08 

207.12 

.0338 

.0177 

$.0144 

• ' 

.039 

.1049 

Santa Cruz . . . 

2G.08 











Alameda . . . 
Connecticut. 

45.60 

986.84 

250.00 

117.87 

367.87 

.0648 

.0493 

.0617 

• • 

.0826 

.259 

Soutli Norwalk . 
Georgia. 

44.40 

486.50 

99.55 

31.25 

130.80 

.0317 

.0199 

.0069 

• • 

.0185 

.0771 

Madison .... 
Illinois. 

G3.00 

365.08 

92.79 

49.28 

142.07 

.0276 

.0257 

.041 

.0016 

.0511 

.147 

Metropolis . . . 

68.40 

, , 

48.24 








• • 

Aurora .... 

120.00 

377.69 

84.01 

50.99 

135.00 

.0257 

.0151 

.0045 

.0028 

.0295 

.0774 

Chicago .... 

888.00 

774.13 

120.80 

91.21 

212.01 

.0274 

.0135 

.0101 


.0386 

.0896 

Elgin. 

Indiana. 

60.00 

400.00 

113.58 

50.00 

163.58 

.0272 

.0153 

.0154 


.0254 

.0834 

Goshen .... 

19.20 

572.92 

141.43 

77.34 

218.77 

.0305 

.0284 

.006 


.0357 

.1009 

Anderson . . . 

86.40 

318.63 

59.96 

43.04 

103.00 

.012 

.0008 

.0054 


.0131 

.0313 

Iowa . 












Fairfield .... 

14.40 

416.66 

68.44 

56.25 

124.69 

.0372 

.0355 

.0147 


.0718 

.1591 

Marshalltown . . 
Kansas. 







.0044 

.0068 


.0271 

.0471 

Council Grove 

16.30 

490.80 

• , 

62.57 






• 

. 

Lyons .... 
Maine. 

32.40 

169.75 

22.42 

22.91 

45.33 






.0536 

Lewiston . . . 

48.00 

333.33 

104.16 

45.00 

149.16 

.0165 

.0083 

.0127 


.0162 

Maryland. 











.0821 

Frederick . . . 

28.80 

520.83 

121.52 

70.31 

191.83 

.0228 

.0114 

.0177 


.0301 

Michigan. 

Bay City . . . 

Minnesota. 

87.00 

413.60 

103.20 

51.57 

154.77 

.0148 

.0102 

.0117 

.006 

.0214 

.0642 


.1054 

F ulda. 

30.00 

166.66 

42.00 

22.50 

64.50 

.0294 

.0326 

.0065 

. , 

.0367 

Luverne .... 

79.20 

123.74 

36.94 

17.10 

54.04 

.0099 

.0211 

.0049 

• a 

.0168 

.0528 

Arlington . . . 

10.30 

291.26 

143.20 

39.32 

182.52 

.0696 

.0348 

.0164 

• 

.0331 

.154 

Sleepy-Eye Lake 

Missouri. 

19.56 

• • 

107.62 








.1324 

Shelbina.... 

39.00 

182.62 

67.44 

26.47 

93.91 

.026 

.0353 

.0314 

.0023 

.0374 

Rock Port . . . 

30.00 

466.66 

87.00 

63.00 

150.00 

.0217 

.0195 

.0076 

.0078 

.0409 

.0975 

Hannibal . . . 

222.00 

211.40 

31.09 

23.07 

54.16 

.0142 

.0071 

.011 

• • 

.0241 

.0565 

Nebraska. 











.2473 

Crete. 

16.30 

582.82 

157.66 

78.68 

236.34 

.081 

.0616 

.0225 

. . 

.0822 

Falls City . . . 

36.00 

250.00 

74.44 

31.25 

105.69 

.0177 

.0145 

.0022 

.0051 

.0166 

.0561 

North Carolina. 

High Point. . . 

New Jersey. 

24.45 

• • 

53.41 








• • 

Madison .... 

198.00 

176.77 

• • 








* * 

New York. 








.0125 


.0236 

.0569 

Dunkirk .... 

50.40 

394.18 

69.53 

49.27 

118.80 

.0091 

.0118 

• 

West Troy . . . 

Westfield . . . 

49.44 

525.88 

127.34 

70.99 

198.33 

.0128 

.0138 

.0051 

.0005 

.018 

.0502 

76.80 

169.27 

77.52 

19.46 

96.98 

.0259 

.0082 

.0425 

• • 

.0188 

.0956 

Ohio. 

St. Clairsville . 

44.00 

225.22 

39.20 

28.40 

67.60 

.0146 

.0048 

.0073 

.0012 

.0204 

.0483 

Painesville . . . 

43.20 

300.92 

80.28 

37.61 

117.89 

.0272 

.0139 

.015 

• • 

.0262 

.0825 

Pennsylvania. 

Fast on . . • . 

64.80 

617.20 

137.45 

70.97 

208.42 

.0156 

.0194 

.0179 

.0038 

.0294 

.086 

Quakertown . • 

56.20 

328.06 

97.24 

38.94 

136.18 

.0246 

.0172 

.0364 


.0313 

.1095 

Texas. 

Galveston . . . 

122.40 

326.80 

135.67 

44.11 

179.78 

.0221 

.011 

.017 

. • 

.0163 

.0664 

Virginia. 

Farmville . . . 

32.40 

370.37 

79.63 

50.00 

129.63 

.029 

.021 

.0042 

• • 

.034 

.0884 

Washington. 

Chehalis .... 

59.40 

252.52 

94.94 

44.52 

139.46 

.0247 

.0343 

.0054 

• • 

.0315 

.096 

Wisconsin. 

Hudson .... 

16.30 

429.44 

92.02 

57.97 

149.99 

.0125 

.0125 

.0167 

• • 

.0261 

.0679 

















































552 


THE ELECTRICAL TRANSMISSLON OE ENERGY. 


plant, in comparison with the cost of manufacturing a similar amount 
of energy by some other means at this station. 

719. To determine the cost of energy delivered by the transmis- 

Table No. 73. 


Cost of Plant and of Operating for Arc-Light Stations. 


Location of Plant. 

24 Private Stations. 

Number of Lamp 
Hours per Annum. 

Cost per Lamp Hr. 
per Annum. 

Cost per Lamp Hr. 

Location of Plant. 

24 Private Stations. 

Number of Lamp 

Hours per Annum. 

Cost per Lamp Hr. 

per Annum. 

Cost per Lamp Hr. 

1. Texarkana, Ark. . . 

3741 

$160.00 

.0428 

13. Lansing, Mich. . . 

2190 

$100.00 

.0456 

2. Jacksonville, Ill. . . 

2190 

96.00 

.0437 

14. Kansas City, Mo. 

3741 

200.75 

.0534 

3. Joliet, Ill. 

3741 

124.00 

.0331 

15. Sedalia, Mo. . . . 

2190 

87.00 

.0398 

4. Peoria, Ill. 

2190 

145.00 

.0662 

16. Springfield, Mo. . . 

2190 

136.00 

.0620 

5. Springfield, Ill. . . 

2190 

137.00 

.0625 

17. Bellaire, O. 

2190 

90.00 

.0410 

6. Streator, 111. . . . 

3741 

96.00 

.0256 

18. Tremont, O. . . . 

3741 

90.00 

.0240 

7. Kokomo, Ind. . . . 

3741 

100.00 

.0267 

19. Hillsborough, O. . . 

2190 

70.00 

.0320 

8. Logansport, Ind. . . 

2190 

100.00 

.0456 

20. Lebanon, Pa. . . . 

1872 

80.00 

.0427 

9. Arkansas City, Kan. . 

1872 

72.00 

.0384 

21. New Castle, Pa. . . 

3741 

80.00 

.0214 

10. Augusta, Me. . . . 

3285 

76.33 

.0232 

22. Dallas, Tex. . . . 

3741 

95.85 

.0258 

11. Bath, Me. 

2237 

125.00 

.0528 

23. Houston, Tex. . . . 

3741 

150.00 

.0400 

12. Grand Rapids, Mich. 

3741 

109.00 

.0293 

24. Parkersburgh, Va. 

3741 

102.00 

.0272 

Averages . 

2922 

$109.27 

.0393 


C/3 

k. 



C/3 



19 Municipal Plants. 

tl Lamp Horn 
:r Annum. 

cl 

c 

as 

S 

CL 

° E 

X 

a, 

S 

a 

u 

<v 

cl 

19 Municipal Plants. 

il Lamp Houi 
r Annum. 

cl 

r-> 

ri 

5 

CL 

° s 

X 

a 

r* 

c 

as 

•J 

u 

<u 

CL 


o »• 
H 

«/) 

o ^ 

(J 

C/3 

o 

U 


o ^ 
H 

O 

u 

c n 

O 

o 

1. Little Rock, Ark. . . 

2920 

$317.00 

.0315 

11. Lewiston, Me. . . . 

2190 

150.00 

.0332 

2. Aurora, Ill. 

2775 

531.00 

.0469 

12. Bay City, Mich. . . 

2190 

210.00 

.0380 

3. Bloomington, Ill. . . 

3741 

333.00 

.0240 

13. St. Joseph, Mo. . . 

2920 

264.00 

.0354 

4. Elgin, Ill. 

3650 

288.00 

.0213 

14. Gabon, O. 

2190 

315.00 

.0331 

5. Moline, Ill. 

3741 

263.00 

.0225 

15. Marietta, O. ... 

1872 

200.00 

.0330 

6. Paris, Ill. 

2555 

160.00 

.0231 

16. Chambersburg, Pa. . 

2190 

556.00 

.0545 

7. Madison, Ind. . . . 

2190 

294.00 

.0428 

17. Meadville, Pa. . . . 

2555 

270.00 

.0311 

8. Topeka, Kan. . . . 

3741 

272.00 

.0347 

18. Titusville, Pa. . . . 

3650 

150.00 

.0158 

9. Bowling Green, Ky. . 

2190 

250.00 

.0365 

19. Galveston, Tex. . . 

2555 

228.00 

.0449 

10. Bangor, Me. . . . 

3741 

250.00 

.0200 





Averages . 

2819 

$279.00 

.0328 


sion plant, the following items must be taken, as affecting the total 
expense : — 

First. The interest and depreciation on the necessary capita! 
invested in improving the water-power, or other source of energy, 

































































TIIE COST OF PRODUCTION AND DISTRIBUTION 553 

and in the purchase of the necessary machinery, engines, dynamos, 
water-wheels, etc., and in the acquisition of real estate and erection 
of buildings required for the generating-station; in other words, the 
total cost of the generating-station. 

720. Second. The cost of obtaining power at the generating-sta¬ 
tion. This item will include rent paid for water-power, or interest 
on the necessary capital invested in the purchase of water-right. A 
similar expense would be the cost of purchase of fuel at a location 
where such a low price for coal could be obtained as would seemingly 
warrant the installation of a transmission plant. 

721. Third. The expense of energy at the generating-station 
is further augmented by the cost of such labor and superintendence 
as may be necessary to operate and maintain the plant. 

722. Fourth. The interest and depreciation on the cost of 
erecting the line between the generating-station and the receiving- 
station. 

723. Fifth. The cost of energy lost in transmission between 
the generating and the receiving station. 

Interest and depreciation on the cost of the machinery, buildings, 
etc., for the receiving-station , do not enter into the expense of 
delivering energy at the receiving-station, for the reason that, were 
any different arrangements made for obtaining electrical energy at 
the receiving-station than that of the transmission plant, a station es¬ 
sentially similar, so far as this cost is concerned, would be necessary. 

Summarized : The cost of energy at the receiving-station, then, 
stands as follows: — 

First. Interest and depreciation upon the capital invested in 
the generating-station. 

Second. Cost of obtaining energy at the generating-station. 

Third. Labor at the generating-station. 

Fourth. Interest and depreciation upon cost of transmitting line. 

Fifth. Losses in line transmission. 

724. To determine the advisability of the installation of a long¬ 
distance plant, it is necessary to compare the probable cost of energy 
delivered to the receiving-station by the long-distance plant, with 
the cost of a corresponding amount, as obtained at this location , by 
any other means. Should the figure obtained for the cost of energy 
by a long-distance plant be equal to that required by the manufac- 



554 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


ture of energy in any other way, it is evident that the long-distance 
plant will stand on precisely equal footing with any other installation. 
Should the amount for production of energy by a long-distance plant 
be less than that by other installations, the long-distance plant will 
be profitable in that proportion. 

725. The ability to produce energy at the receiving-station will 
be limited to the power derived by means of a steam-engine. Cases 
where wind, tidal power, or other methods would be available, are so 
infrequent that they may be discarded without seriously affecting 
the result, and attention confined solely to the production of energy 
at the receiving-station, by means of a steam-engine, in contra¬ 
distinction to that obtained by the transmission plant. The cost of 
the production of energy by means of steam-power is tolerably well 
ascertained. The cost of energy will vary with the kind of engine, 
the price of coal, the rate of interest and depreciation upon the capi¬ 
tal invested in the plant, and cost of necessary labor. In Table No. 
74 a series of curves with necessary data is given, for determining 
the capital to be invested in a steam-plant, the cost of perpetual 
maintenance of the same, and the production of power. The Table 
is divided into four parts. 

First. A schedule giving the cost of steam-plant per horse¬ 
power at the engine and per kilowatt of energy delivered at the 
terminals of the generator. In this latter column the values are 
assumed for engines working at a reasonably steady full load, with 
an efficiency of 90 per cent in the generator. The figures are those 
which would apply to fairly large installations, say from 250 horse¬ 
power upwards, and would prevail for most locations east of the 
Mississippi River, in this country. Special charges necessitated by 
locations out of the ordinary have not been considered. The 
schedule is arranged to embrace seven different styles of engines, 
considered to be those which are more likely to be used. 

726. The second division of the Table embraces a set of curves 
arranged for the purpose of calculating the interest and depreciation 
to be allowed upon the steam-plant. A separate line is given for 
each type of engine, the horizontal axis being scaled for interest 
and depreciation, while the vertical axis gives the amount to be 
assessed per horse-power per annum, for varying rates on the 
interest and depreciation scale. 


THE COST OF PRODUCTION AND DISTRIBUTION. 


555 


The third part of the Table is devoted to the cost of fuel and 
supplies in dollars per horse-power per year. 

The horizontal axis here embraces the cost of coal in tons, of 
2,240 pounds, from $2.00 to $10.00 per ton, while the vertical axis 
indicates the corresponding cost per horse-power per annum. It 
should be here noted that the lines are so drawn as to include the 
cost of the ordinary amount of oil and other minor supplies which 
would be naturally required in a steam-plant. While these values 
are not absolutely correct, as a slight variation in the cost of the 
minor supplies, in comparison with the cost of coal, would make 
slight changes, it is considered that it is sufficiently accurate for 
ordinary purpose of estimate. 

The fourth division of the Table applies in a similar manner to 
rates of wages for engineer and fireman. On the horizontal axis will 
be found the rates per day for engineer and fireman, two scales, one 
for each class of labor, being indicated. The vertical axis gives the 
wages cost per horse-power per annum. In each of the divisions a 
separate line will be found for each kind of engine, which may be 
readily identified on the schedule by means of a corresponding initial 
letter, used in each of the divisions. To use the Table, select on 
the horizontal axis the value required ; follow a vertical line to its 
intersection with the line indicating the kind of engine proposed to 
install, and then follow a horizontal line to the left to the vertical 
axis, finding the value desired. This Table forms a convenient 
means whereby the engineer may rapidly determine the probable 
cost of energy per horse-power per annum, as developed by a steam- 
plant erected at the receiving-station. It is now necessary to as¬ 
certain the cost of energy delivered at the receiving-station, when 
obtained through the medium of long-distance transmission, and 
compare this with the cost of energy as obtained by means of the 
steam-plant. 

727. The factors composing the cost of energy at the receiving- 
station , as delivered by the transmission plant, are as follows : — 

First . Interest and depreciation on cost of generating-station. 

Second. Cost of power at generating-station. 

Third. Cost of labor at generating-station. 

Fourth. Interest and depreciation on cost of line. 

Fifth. Cost of energy lost in the line. 


556 


THE ELECTRICAL TRANSMISSION O*' ENERGY. 




Note. — For detailed information, see Sheet of Curves in pocket, marked Table No. 74, Sheet 1. 




























































Interest and Depreciation, in Dollars 




THE COST OF PRODUCTION AND DISTRIBUTION. 557 

I 


Table No. 74 (Continued) 


Cost of Installing; and Maintaining; Steam Plant 


SHEET 2 



Interest and Depreciation, in per.cent. 


vw fe a 












































































































































































































































Sheet 3 


558 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


Table No. 74 ( Continued ). 

Cost of Installing and Maintaining Steam-Plant. 



*yV3A d3d cH d3d SSIlddflS QNV “ODd 30 1SOO 


COST OF COAL IN DOLLARS PER TON (2240 LBS.) 



























































































































































































































































Sheet 4. 


THE COST OF PRODUCTION AND DISTRIBUTION. 


559 


Table No. 74 ( Continued ). 


Cost of Installing and Maintaining Steam-Plant. 
< CO O Q wu.0 



Wages in dollars per day. 




















































































































































































































































500 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


For this purpose, it is convenient to refer to Table No. 75. 
The use of this table, as it is slightly complex, will be best com¬ 
prehended by means of an example. 

Assume the following data : — 


a. Cost of generating-station per horse-power . . $150.00. 

1. Interest and depreciation on generating-station 

per annum. lb per cent. 

2. Cost of water per horse-power per annum . . $15.00 

3. Cost of labor. $2.50 per day. 

b. Cost of line per mile.$1800.00. 

c. Length of line. 5 miles. 

4. Interest and depreciation on cost of line per 

annum. 15 per cent 

5. Loss in line. 20 per cent. 

d. Power transmitted. 400 H. P. 


To find cost of energy at receiving-station. 

728. Refer to Table No. 75, finding, on the left-hand side, along 
the vertical axis, two scales, one labeled “ Cost of Generating-Plant 
per H. P.” Taking this scale, proceed to $150.00 ( a ), the assumed 
cost of the plant per horse-power. From $150.00 follow a horizontal 
line (this example mayi be readily traced by following the dotted 
lines upon the diagram, which have no reference to any calculations 
excepting the particular example now under consideration) to the 
point of intersection of the horizontal with the diagonal line marked 
“Interest and Depreciation” (1), and labeled “10 per cent,” the as¬ 
sumed value. The amount of interest and depreciation is then found 
by following a vertical line downward to the lower scale, marked 
“ Interest and Depreciation on Generating-Plant per H. P.,” giving 
$15.00 as the interest and depreciation per horse-power of plant 
capacity per annum. It is now necessary to take into consideration 
the cost of water per annum, which is assumed to be $15.00 (2). 

729. P'rom the point of intersection of the horizontal through 
$150.00, with the interest diagonal 10 per cent follow a vertical 
line upwards to the intersection of the diagonal under “ Cost of 
Water-Power per H. P.,” labeled “$15.00.” Then follow a horizon¬ 
tal line to the right to the left-hand scale on the right-hand side of 
the diagram, — the scale labeled “Interest and Depreciation on the 
Generating-Plant plus the cost of Water-Power per II. P.” The 









THE COST OF PRODUCTION AND DISTRIBUTION 561 

value here given, $30.00, is the sum of the first and second items. 
To include the cost of labor (3), return to the intersection with the 
“ Cost of Water diagonal through $15.00, follow the horizontal line 
to the right to the intersection of the “ Cost of Labor per Day ” 
diagonal, labeled $2.50. At this point follow a vertical line to the 
extreme upper scale of diagram, labeled “ Interest and Depreciation 
plus Cost of Water, plus Cost of Labor, or total Cost at Generating- 
Station per H. P.,” finding the total value to be $32.50 as the cost 
per horse-power per annum at the generating-station. It now 
remains to find and add to this amount the cost of the energy lost in 
transmission (5) between the generator and the receiving-station, and 
the interest and depreciation on the cost of the line, in order to get 
the total expense of energy at the receiving-station. 

730. From the intersection of the previous horizontal line with 
the diagonal for the “Cost of Labor per Day,” marked “$2.50,” fol¬ 
low a vertical line downward to intersection with the diagonal under 
the heading “Losses in Line,” labeled “20 per cent.” From this 
point follow a horizontal line to the right, to the left-hand scale on 
the right-hand side of the diagram, headed “ Interest and Deprecia¬ 
tion plus Cost of Water, plus Cost of Labor, plus Losses in Line.” 
Here the value of $39.00 will be found as the cost per horse-power 
per annum of energy delivered at the receiving-station by the trans¬ 
mission plant, exclusive of interest and depreciation on the cost of 
the line, which figure it is now necessary to ascertain. The previous 
amount, $39.00, must be carefully noted, as it is necessary to 
add the amount of the interest and depreciation on the line to it. 
To find this latter figure, return to the extreme left-hand vertical 
scale of the diagram headed “ Cost of Line per Mile in Dollars ” (b). 
Selecting the figure $1800.00, the assumed cost of the line per mile, 
follow a horizontal line to the right to the intersection of the diagonal 
marked (15 per cent) (4), the assumed rate of interest and depreci¬ 
ation on the line, under head “ Interest and Depreciation.” From 
this intersection follow a vertical line upwards to the lower top scale 
marked “ Interest and Depreciation on Line per Mile,” obtaining the 
value $270.00 as interest and depreciation on the line per mile of 
length. This figure is, evidently, not the total amount necessary to 
obtain, as the length of the line is not included. From the upper 
left-hand corner of the diagram will be seen the number of radiating 


562 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


diagonal lines headed “Length of Line in Miles” ( c ). From the 
intersection of the previously mentioned vertical with the diagonal 
headed “5 Miles,” follow a horizontal line to the right, obtaining, on 
the scale marked “ Interest and Depreciation on the Whole Line,” 
the figure $1350.00 as the amount of this charge. As the entire 
calculation is made per unit of power, it is evident that the charge 
for interest and depreciation on the line must be divided by the 
total amount of power transmitted in order to obtain the proper pro¬ 
portional charge per unit of energy supplied. To secure this result, 
the last obtained amount must be divided by the amount of power 
transmitted, namely, 400 horse-power ( d). To accomplish this, return 
on the horizontal line through $1350.00, until an intersection is 
obtained with the diagonal marked “400 H. P.” Here follow a 
vertical line to the lower top scale of the diagram marked “ Interest 
and Depreciation on the Whole Line per Horse-Power,” finding a 
value of $3.37 as the amount for the interest and depreciation on the 
line per unit of power, to be added to the previously obtained cost of 
$39.00, making a total cost of $42.37 per annum per horse-power, 
delivered at the receiving-station. 

731. In this example the process has been given in extenso 
step by step, in order to familiarize the reader thoroughly with the 
workings of the diagram, and to show that the process may be 
stopped at any desired step, and used to obtain the value of any 
successive set of items. If it is wished to complete the entire calcu¬ 
lations without any reference to the intermediate steps, the process 
is as follows : — 

732. Find the cost of the generating-station per horse-power on 
the left-hand scale of diagram. In this example, start at $150.00, 
follow a horizontal line to intersection with the “ Interest ” diagonal; 
from this point follow a vertical line to the intersection with “ Cost 
of Water per H. P.” diagonal, then a horizontal line to the “Cost of 
Labor per Day ” diagonal, then vertical line to the intersection with 
diagonal headed “Losses of Line,” then horizontal line to the right 
to the left-hand scale on the right-hand side of diagram, finding the 
figure $39.00 as the “ Cost of Power at the Receiving-Station.” 

733. In a similar manner, to obtain the value for “ Interest and 
Depreciation on Cost of Line per H. P.,” start at $1,800.00 on left- 
hand scale on diagram, follow a horizontal to intersection with the 


THE COST OF PRODUCTION AND DISTRIBUTION 563 

“ Interest diagonal, then the vertical to intersection of diagonal 
giving “ Length of Line,” then vertical to lower scale on top of 
the diagram, giving S3.37 as the total cost per unit of power, for 
“ Intel est and Depreciation on the Line.” Add these two figures to 
obtain the desired result. 

From slight consideration it is evident, by these tables, problems 
involving the commercial aspect of long-distance transmission may 
be rapidly solved, providing the necessary data for obtaining the 
constants are at hand. 

734. Economical Conductor Section. — In long distance trans¬ 
mission, the cost of the line rises to be one of the most important 
factors, if not the principal one, in the installation. 

To determine the most economical area for the conductor, the 
principles given in Chapter IX. should be used, and may be directly 
applied to the greatest advantage. The equation there given for 
finding the proper conductor area is — 

U = a ftS -f- — . 

In this equation three coefficients must be considered ; namely, 
a, (3 , and A. 

By the process of differentiation a disappears ; so to determine 
the value of S, the quantities (3 and A only need enter into considera¬ 
tion. The term (3 is substituted for the expression L [b (i + d t ) -f- 
b' (i + d c ) ], involving the interest and depreciation to be allowed 
upon the cost of the conductor, and upon the structure used for 
supporting or protecting it. Two rates of interest and depreciation 
were allowed, as in the most refined calculations, especially those 
involving the cost of conduit structures, the interest and depreciation 
assessed upon the conduit would be different from that on the con¬ 
ductor. For ordinary purposes of calculation, as an abridgment of 
the process, the two rates may be assumed the same, and the value 
of (3 considered to be L (b - f- b') (i -f- d c ). The term A involves the 
amount of current transmitted, the resistance and length of the line, 
the interest and depreciation allowed upon the cost of the station 
per unit of output, and the cost of producing the energy lost in the 
line; adopting the notation of Chapter IX., A = / 2 p L [FK + K' 

( l + d s ) ]• 

735. For the purpose of facilitating calculations of the most 


564 


THE ELECTRICAL TRANSMISSION OE ENERGY. 


economical conductor cross-section, Tables Nos. 76, 77, and 78 are 
presented for determining the values of the above coefficients, giving 
a solution directly of the equation x = Va //?. 

Tables Nos. 77 and 78 are arranged in two parts — part B of 
each Table being laid out to a reduced scale, as compared with part 
A. As the scales in all of the Tables are decimal, the range of the 
Tables may be extended in any direction by multiplying or dividing 
by any power of 10. By means of the decimal arrangement and the 
double sets of values given, all problems within ordinary ranges may 
be readily solved. As the use of the Tables is a little complicated, 
an example will perhaps best elucidate their application. 

Returning to the data given on p. 560 used to exemplify the use 
of Table No. 75, and adding to the constants there assumed, the 
amount of current to be transmitted through the line, 200 amperes, 
and the length of time this current flows through the line, 3,000 
hours per annum, let it be required to find the most economical 
cross-section for the conductor. 

736. The Tables have been calculated, by assuming the length 
of the line to be one mile of double circuit; that is, a mile away from 
the station and a mile back, making the total actual length of the 
line two miles. It will also appear that the most economical con¬ 
ductor cross-section, as determined for a mile of double circuit, will 
equally apply to a line of any length, for reason that, as the resist¬ 
ance increases directly in proportion to the length of the line, the 
amount of energy wasted and the interest and depreciation on the 
cost of the line will correspondingly increase in the same direct pro¬ 
portion. 

737. Table No. 76 serves to determine the two constants inside 
the brackets ; namely, FK, and K'(i -f- d s ). To determine the value 
of this latter quantity, look for the cost of the generating-station 
along the top scale of diagram labeled “ Cost of the Generating-Sta¬ 
tion per H. P.,” or K'. In the example under consideration, #150.00 
is assumed for the cost of the station, while the interest and depre¬ 
ciation (i -f- d^} is given on the diagonals running downward from 
the right-hand upper corner. From #150.00 or “Cost of Station” 
follow a vertical downward to the intersection of the diagonal marked 
“ ( i + d s ) ” for the assumed rate of 10 per cent, then follow a horizon¬ 
tal line to the right, to the left-hand scale marked “ K'( i + d s )," here 



THE COST OF PRODUCTION AND DISTRIBUTION 


565 


finding the value of “ $15.00 ” as the amount of this expression. 
Note this value. Now, to determine FK, having the annual cost of 
producing energy per horse-power, as obtained from Table No. 75. 
It must be recollected that this cost per horse-power, as given by 
Table No. 75, is based upon operating the station 3,000 hours per 
annum. In order to find the cost per horse-power hour, select on the 
lower horizontal scale, labeled “ Cost of Energy at the Generating- 
Station per H. P.,” the cost gathered from Table No. 75, follow a 
vertical line upward to intersection with diagonal line marked “ 3,000 
hours,” then follow a horizontal to the right-hand scale on the right- 
hand side of the diagram, finding the desired amount on the scale 
marked “ Cost of Energy at Generating-Station per H.-P. hour!' In 
the example under consideration, from Table No. 75, a cost of 
$32.50 was obtained as the “Cost of 1 H.P. for 3,000 hours.” Se¬ 
lect this point on the lower scale, follow a vertical line upward to 
intersection with diagonal labeled “3,000 hours,” then follow a hori¬ 
zontal to the right, to the right-hand scale, the value of $.0108 is 
found as the “ Cost of one H.-P. hour.” FK is the cost per horse¬ 
power, multiplied by the time of operation, and is obtained from the 
Table by following a horizontal line to the left from the cost per horse¬ 
power hour on the right-hand scale till the horizontal intersects the 
diagonal marked with the number corresponding to the annual time 
of operation. Thus, supposing the plant to operate for 5,000 hours, 
following diagonal from the right-hand scale through .0108 to the 
intersection of the diagonal labeled “5,000 hours,” then a vertical 
downward to the horizontal scale, the value of $54.16 is found for 
FK. Continuing, however, the original example on the supposition 
that the plant operates for 3,000 hours, the value of $32.50 is found 
for FK. Note this value. The Table thus gives the values of the 
two quantities inside the brackets; namely, FK and K' (i + d s ). 
These two values must now be added, giving $47.50 as the total of 
the quantity inside the brackets. 

738. Now, turning to Table No. 77, the top scale is labeled 
value of FK -f K'(i + d s ). The left-hand scale gives the values of 
PpL, while the lower scale gives the values of F 2 pL x [FK+ K'(i+d s )], 
or the value of A. On the top scale of the diagram find the value of 
FK+K'(i+d s ), as obtained from Table No. 76. Connect this point 
with the origin at the lower left-hand corner by a diagonal line (see 


566 


THE ELECTRICAL TRANSMISSION OF ENERGY. 


dotted line). The value of Pp must now be obtained. The con¬ 
ductor in this example is assumed to be soft copper, to operate at a 
temperature not exceeding 30° C. Find upon the lower scale of the 
diagram the temperature of the conductor, then follow a vertical line 
upwards to the intersection with the diagonal labeled “ 200 amperes 
S. C.” (soft copper). Follow a horizontal line to the left from this 
intersection to the left-hand scale, from which the value of I 2 pL is 
obtained as 5. From the intersection of this horizontal line with the 
diagonal to the origin drawn from the value of FK + K'(i -f- d s ), on 
the top scale, follow a vertical line downwards to the lower scale 
labeled “Value of P-pL [FK + K' (i -f d s )]f obtaining here the value 
of this expression as 250, or the value of A. The dotted lines on the 
Tables serve to show the course followed in the solution of this par¬ 
ticular example, but have no reference to the solution of any other. 
The dotted lines have been drawn on both parts of each diagram, in 
order to show that the same result is obtained on each. The opera¬ 
tor should use that section of diagram which will give the most 
advantageous scale. Now, turning to Table No. T8, find upon the 
right-hand vertical scale, headed “Cost of Line per Mile,” the amount 
of capital invested in the line, recollecting that the mile here referred 
to is two actual miles of circuit. In this case the cost of the circuit 
mile is $1,800. Follow a horizontal from this figure to intersection 
with the diagonal giving the determined rate of “ Interest and Depre¬ 
ciation,” in this example 15 per cent being selected. From this 
intersection follow a vertical line upward to the top scale of the dia¬ 
gram, here finding the value of L [ b{i-\-dj) + b' (i + d c )\ or (3. The 
value here obtained is $270.00. Connect this point by a diagonal with 
the origin at the lower right-hand corner. From Table No. 77, the 
value of A was found to be 250. On the lower horizontal line, marked 
“Value of A,” find 250. At this point erect a perpendicular until it 
intersects the diagonal previously drawn from the point on the top 
scale, giving the value of (3 to the origin. The point of intersection 
of the vertical and this diagonal is, evidently, the value of A / (3. 
From this intersection follow a horizontal line to the left, until the 
curve C is intersected, then follow a vertical downward to the lower 
horizontal scale marked “Value of 5,” here finding T %% of a sq. in. 
as the most economical value of the cross-section of the con¬ 
ductor. 


THE COST OF PRODUCTION AND DISTRIBUTION '. 


567 


Though the process of using the Tables, as here described, may 
seem somewhat complicated, experience gained from the solution of 
half-a-dozen examples will enable the operator to determine the most 
economical cross-section of conductor in one-quarter the time that is 
required to read the description. 

By means of the graphical methods thus outlined, the designer 
may rapidly determine the best cross-section for the conductors of a 
transmission plant under any of the usual limiting conditions. A 
careful comparison should always be instituted between the section 
thus ascertained and that indicated by each of the various other gov¬ 
erning factors that enter into every distributing problem ; for the 
most economical conductor section is by no means always the most 
advisable one to employ. 

In the distribution of energy by means of electricity, the prin¬ 
ciples outlined form a ground-work sufficient to enable the designer 
to so utilize materials and energy as to attain the desired result. 
Facts and laws are, however, like tools, the value of the product 
depending largely on the skill of the workman. 


THE END. 



















































\ 


INDEX 


ART - PAGE. 

500 Accomplishment of Best Service, De- 



sign for. 

. . 391-392 

659 

Accumulators, Sub-station . 

. . 498-499 

660 

Accumulator Distribution . 

.... 499 

661 

Accumulators, Means of Regulation by 



499-500 

655, 661 Accumulators. 



714 Actual Cost of Producing Electrical 

Energy. 547-549 

412 Addition of Vectors . ...... 337 

497 Additional Ton of Copper, Table of 

Cost of . 390-391 

459-460 Adjacent Bodies, Effect on Capacity of 



Circuits . 

370-371 

211 

Aerial and U. G. Systems, Connection 


of. 

195-197 

19 

Aerial Lines, Tension .... 

. . 31 

21 

Aerial Circuits, Construction of . 

. . 36 

22 

Aerial Lines. 


50 

Aerial Cables, Suspension of . . 

. 68-69 

321- 

-325 Aerial Lines, The Capacity of . . 

263-265 

326 

Aerial Lines, Inductance of . . 

. . 265 

378 

Aerial Cables, Heating of . . . 

. . 309 

629 

Aerial and Paneled Conductors, 

Heat 


Limits for . 471 

, 472, 475 

107 

Air Expansion Arrester .... 


123, 

131, 147 Alternating Current System, 

Ins. 


Regulations for .... 127, 

132, 137 

304 

Alternating Currents, Measurement of 


Inductance by Means of . . . 

. . 255 

308 

Alternating Current Potential, Measure- 


ment of . 



308-316 Alternating Current Circuits, Measure¬ 
ments on. 257-259 

309 Alternating Current Circuits, Measure¬ 
ment of Currents.257 

311 Alternating Current Circuits, Two Volt¬ 
meters, Power Measurement . . . 258 

311 Alternating Current Circuits, Measure¬ 

ment Power by 3 Ammeters .... 258 
380-460 Alternating Currents, Conductors for 

311-371 

382 Alternating Currents, Classification of 


Effect on Conductors.312 

382 Alternating Currents, Skin Effect in 

Conductors for.312 

383 Alternating Current Circuits, Current 

Density in.312 


ART. 

PAGE. 

383 

Alternating Current Conductors, Thick- 


ness of Shells Effected by . 

. . .314 

383 

Alternating Circuits, Table of 

Virtual 


Resistance. 


391 

Alternating Circuits, Expenditure of 


Energy in. 


18 

American Wire, Specifications 

. . 28«31 

714 

America, Cost of Producing Electricity 


in. 

. 551-552 

226 

Ammeter, Weston. 


283 

Ammeter, Measurement 

Current 


Strength of. 


56 

Anchor Guy Stubs .... 


37 

Anchor Poles. 


37 

Anchor Poles, Iron .... 

... 47 

37 

Anchor Poles, Dimensions of . 

. . 53-57 

98 

Anchors. 


533 

Anti-Parallel Feeding . . 


542- 

543 Anti-Parallel Feeding, Conical Conduc- 


tors. 

. 420-421 

540 

Anti-Parallel Feeding, Cylindrical Con- 


ductors.418-420 

128, 130, 142 Arc Circuit Conductors, 129, 132, 136 
128 Arc Lamp, Insurance Regulations for . 129 
130 Arcs on Constant Potential Circuits, In¬ 
surance Regulations for.132 

637 Arc Lamps on Constant Potential Cir¬ 


cuits .. 

666 Arc Lamps, Transformers for .... 503 

562 Areas, Relative, covered by Multiple- 

Wire Systems.435 

194 Armored Cables.175 

104 Arresters, High Resistance.114 

108 Arrester, Wurtz . ..117 


105 Arrester, Magnetic Blow-out . . . .115 

105 Arrester, Thompson-Houston . . . .115 

106 Arrester, Edison Lightning.116 

106 Arrester, Mechanical Magnet . . . .116 


107 Arrester, Westinghouse.116 

108 Arrester, Non-arcing, Wurtz . . . .117 

109 Arrester, Condenser.118 

109 Arrester, Discriminating.118 

109 Arrester, Non-arcing Continuous Cur¬ 
rent, Wurtz.119 

112 Arrerters, Lightning, for Cables . . . 122 

113 Arresters, Lightning, for Sw. Bds. . . 123 

114 Arresters, Sneak Current.124 

111 Automatic Cut-outs.120 















































570 


INDEX . 


ART. 

514 

395-396 

219 

14 

122 

270 

270 

272 

274 

275 
387 
578 
581 
189 
682 

459-460 

61 

74 

76-77 

81 

239-240 

46 

60 

18 

18 

18 

203 

351-356 


Automatic Cut-outs 
Average Values of 


PAGE. 

.398 

Circuit Constants 

322-324 

Ballistic Galvanometer .... 205-206 

Bamboo as an Insulator.17 

Batteries, Insurance Regulations for . 126 
Battery Resistance, Measurement of . 239 
Battery Resistance, Measurement of, by 

Voltmeter.239 

Battery Resistance by Deflection . . . 240 

Battery Resistance by Condenser . . 240 

Battery Resistance by Equal Deflection 241 

B, Definition of.317 

Best Number of Feeds.446 

Big Cotton Wood Plant.519 

Blackpool Conduit.171-172 

Blue Lakes Plant.519 

Bodies, adjacent, Effect on the Capacity 

of Circuits. 370-371 

Bolts, Cross-Arm.74 

Bonding Rail.80-82 

Bonding-Resistance of, Rail . . . 83-84 

Bonds, Railway, Size of. 86 

Boyer’s Speed Recorder .... 221-222 

Brackets.64 

Braces, Cross-Arm.74 

British Post-Office, Specifications . . 26-27 

British Wire, Specification .... 26-27 
British Specifications for Iron Wire . . 28 
British Post-Office, Telephone Cable . 188 
Branch Circuits, Description of Current 
and Potential. 282-286 


ART. 

181 

170 

504 

570-578 

620-621 

613-630 

623 

625-629 

727-738 

647 

126-154 

245 

288-292 

290 

291 

292 

321-325 

382 

384 

402-405 

427 

450-459 

459-460 

459-460 


PAGE. 

Callander Solid Conduit.160 

Callander, Weber Conduit, The • . . 147 

Calculation of Loads.394 

Calculation of Feeders .... 444—446 

Calculation of Distributing Mains . 467-468 

Conducting System in Multiple Arc, 

General Design for. 463-472 

Calculation of Feeds.4C9 

Calculation of Inside Wiring . . 470-471 

Calculation, Tabular, for Cost of 

Line'. 560-567 

Calculations for Compensators . 490-491 

Capacity of Wires, Insurance Regula¬ 
tions for.. . 128-139 

Capacity.224 

Capacity Measurement .... 246-250 

Capacity, Estimation of, by Thomson’s 

Method.248 

Capacity, Measurement of, by Gott’s 

Method.249 

Capacity, Measurement of, by Divided 

Charge . 249-250 

Capacity of Aerial Lines, The . . 263-265 

Capacity.312 

Capacity.315 

Capacity, Effect of. 329-331 

Capacity, Effect of.346 

Capacity, Inductance, and Resistance, 

Circuits containing. 365-371 

Capacity of Circuits as Modified by Par¬ 
allel Wires. 370-371 

Capacity of Circuits, Effect of Adjacent 


214 

Bridge, Slide Wire. 

. 201-202 

12 

Carrying Capacity of Paneled Wire 

. 12 

175 

Brooks Conduit. 


119 

Care and Attendance, Insurance Regula- 

189 

Buda-Pesth Conduit .... 

. 170-171 


tions for. 

. 126 

16 

Cable, Flexible. 

. . 18-21 

131 

Car Wiring, Insurance Regulations 

112-115 

Cable, Switchboard, Protectors 

. 122-124 


for. 

. 133 

112 

Cable Protectors. 


227 

Cardew Voltmeter. 

. 211 

193 

Cable Sheaths for Alternating Currents 174 

79 

Cast Railway Joints. 

. 85 

194 

Cables, Armored. 


19 

Catenary, The, Equations of . . 

. 32 

195 

Cables, Siemens. 


169 

Cement-Lined Iron Pipe Conduit 

. 146 

198 

Cables, Telegraph. 


88 

Center-Pole Construction . . . 

. 91 

199 

Cables, Submarine. 

. 183-185 

88 

Center-Pole Railway Construction, 

. 91 

201 

Cables, Paper,. 

. . .186 

91 

Center-Pole Construction . . . 

. 96 

201 

Cable Transmission .... 

. 186-188 

568-574 

Central Station Location .... 

439-442 

202-210 

Cables, Telephone. 

. 188-194 

573 

Center of Distribution and Location 

of 

203 

Cable, Telephone, British Post-Office . 188 


Feeders. 


204 

Cable, Patterson, Telephone . 

. 188-189 

460 

Character of Dielectrics .... 


205 

Cables, Glover, Telephone . . 

. 189-190 

171 

Chenowith Conduit, The.... 


206 

Cables, Fowler-Waring, Telephone . . 190 

10 

Circular Mil, The. 

. . 8 

207 

Cable. F e 1 1 e n-Gu i 11 e aum e, 

Tele- 

16 

Circular Millage of Combinations 

of 


phone . 

. 191-192 


Wire 000 to No. 3. 

. 22-24 

208 

Cable, Beaded, Hermann, The, 

Tele- 

53 

Circuits, Power. 

. 72-76 


phone . 

. 192-193 

72 

Circuits, Electric Railway . . . 

. . 77 

209-210 

Cable Joints and Splices . . . 

. 193-195 

73-85 

Circuit, Railway Return .... 

. 77-90 

211 

Cable Heads. 


75-77 

Circuit-Rails as Railway Return . 

. 82-84 

377 

Cables, Conduit, Heating of 

. . .308 

115-162 Circuits, Insurance Regulations . 

125-140 

33-35 

Calculations for Pole Strength. 

. . 41—45 

185 

Circuits, The Introduction of . . 

167-168 

240 

Calculation for Boyer’s Speed Recorder 222 

196 

Circuits, Edison. 

178-182 




























































INDEX . 


571 


ART. 


PAGE. 


197 Circuits, The Farranti .... 182-183 

200 Circuits, Power Distribution . . 185-18G 

308-316 Circuits, Alternating Currents, Measure¬ 
ments on . 257-259 

391 Circuits, Alternating, Expenditure of 

Energy in.. 

395-396 Circuit Constants, Average Values 

of. 322-324 

397-398 Circuits Containing Resistance and In¬ 
ductance . 324-325 

405- 407 Circuits with Capacity, Solution of En¬ 

ergy Equation for. 331-333 

406- 409 Circuits with Capacity, Solution of 

Energy Equation for, Discussion 
of. 332-333 

407- 409 Circuits Containing Resistance, Induct¬ 

ance, and Capacity, Energy Equa¬ 
tion, Discussion of. 333-335 

419 Circuits, Simple, with One Resistance 

and One Inductance in Series, Electri¬ 
cal Properties of. 340-341 

426 Circuits, Simple, with One Resistance 

and One Capacity in Series, Electri¬ 
cal Properties of. 346-348 

428 Circuits, Simple, containing Resistance 

and Capacity in Series, Graphical 
Solution of Electro-motive Force . . 347 

429 Circuits, Simple, containing Resistance 

and Capacity, Variable Resistance 
in . 348-349 

430 Circuits, Simple, with Several Resist¬ 

ances and Capacities in Series, Elec¬ 
trical Properties of.349 

431 Circuits, Simple, containing Resistance, 

Inductance, and Capacit]' in Series, 
Electrical Properties of . . . 349-350 

432 Circuits, Simple, with Several Resist¬ 

ances, Inductances, and Capacities in 
Series, Electrical Properties of . 350-351 

433 Circuits containing Resistances, Induct¬ 

ances, and Capacities in Multiple Arc, 
Electrical Properties of . . 351-354 

436 Circuits Containing Mutual Inductance, 

Properties of. 357-360 

440-449 Circuits Containing Resistance and In¬ 
ductance, Impetance Tables for, 360-365 
450-459 Circuits Containing Resistance, Induc¬ 
tance, and Capacity. 365-371 

459-460 Circuits Capacity, Effect of Adjacent 

Bodies on. 370-371 

459-460 Circuits Capacity, as Modified by Par¬ 
allel Wires. 370-371 

463 Circuits, Series, Classification of . 372-374 

464 Circuits, Constant Current with Genera¬ 

tors and Receivers at Fixed Distances, 373 

466 Circuit, Main Current Density . 374-376 

467 Circuits, Series, Economical Conditions 

. . 376-377 

497 Circuits, Series, Conductor Tables for, 

388-389 


ART. 


PAGE. 


516-519 Circuits, Series, Design for . . . 398—401 

521 Circuits, Constant Current, Embracing 

Generators and Receivers at varying 

Distances.401 

534 Circuits, Parallel Distribution of, Poten¬ 
tial in.412 

637 Circuits, Constant Potential, Arc Lamps 

on.482 

668 Circuit Wiring, Secondary, Transformer, 505 


680 

Circuit, Long Distance, Typical . 

. . 517 

382 

Classification of the Effect of Alternat- 


ing Currents. 


463 

Classification of Series Circuits 

372-374 

132 

Clear Work, Insurance Regulations for, 130 

530 

Closet System. 

410-111 

706 

Coal Consumption per Watt Hour 

541-542 

302-307 

Coefficients, Inductance, Measurements 


of. 

254-256 

307 

Coefficients of Mutual Inductance, Meas- 


urement of. 

. . 256 

401 

Coefficients of Inductance . . . 

327-329 

182 

Cologne Conduit. 


13 

Composite Wire. 


16 

Combination Wire Table . . . 

. . 24 

37 

Composite Poles. 

. 52-57 

46 

Come Alongs. 


372 

Commercial Fuse Wire, Table for 

. . 300 

418 

Composition and Resolution of Electro- 


motive Forces. 

338-339 

584 

Compensator. 

449-452 

586 

Compensator in Railway Work 

. . 452 

016 

Compensator on Three-Wire System 

. 490 

047 

Compensators, Calculations for 

490-491 

718-738 

Commercial Considerations of Trans- 


mission Problems. 

550-565 

21 

Construction, Line. 

. . 36 

21 

Construction, Aerial Circuits . . 

. . 36 

68 

Construction Details. 


74 

Construction, Ground Wire . . . 

. . 80 

109 

Condenser Arrester. 

. . 118 

109 

Continuous Current Arrester . . 

. . 119 


124, 126, 127, 130, 131, 135,149, 151, 154, Conduc¬ 
tors, Insurance Regulations for, 127, 

128, 130, 131, 132 
134, 137, 138, 139 

130-136 Conduit, Interior, Insurance Regulations 


for . 131-134 

163 Construction of Underground Circuits . 141 

164 Conduits, Classification of.141 

165 Conduit, Valentine.142 

166 Conduit, Wyckoff.143 

166 Conduit, McDonald.143 

167 Conduit, Paper.144 

168 Conduit, Zinc Tubing.145 


168 Conduit, Iron Pipe in Asphalt Concrete, 145 
168 Conduit, Wrought-Iron Pipe in Hy¬ 


draulic Cement ..144 

168-169 Conduits, Pipe.144-147 

169 Conduit, Cement-Lined Iron Pipe . . 146 

170 Conduit, Cal'.ander-Weber . ... 147 










































572 


INDEX. 


ART. 

170 

191 

171 

17U-174 

173 

174 

175 
17G 
177 
17S 
179 
ISO 
181 
182 
182 

188-193 

189 

189 

192 

193 

194 
194 
196 
211 


220 

239-231 

231 

269 

274 

329 

329-379 

329-379 

343-349 

349 

350 


357 

360-363 

360-363 

365 

379 

376 

389-460 


382 

382 


464 

467 

480 

483 

497 


Conduit, The Dorset . . 
Conduit, Love Railway . 
Conduit, The Chenowith 
Conduit, Terra-Cotta, The 


PAGE. 

. . 147 
172-173 
. . 147 
148-152 

Conduit, Terra-Cotta Separate Duct . 150 

Conduit, The Crompton .... 152-154 

Conduit, Brooks.155 

Conduit, The Johnstone .... 156-157 

. 157 

. 158 

. 159 

. 160 

. 160 

. 162 

. 162 

169-174 


Conduit, Kennedy, The .... 

Conduit, The St. James, London. 

Conduits, The Parisian Systems . 

Conduits, Inflexible. 

Conduit, Callendar Solid . . . 

Conduit, Cologne. 

ConduP, Zurich. 

Conduits for Electric Railways 

Conduit, Buda-Pesth.170-171 

Conduit, Blackpool Railway . . 170-171 

Conduit, Lenox Avenue Railway . 173-174 

Conduits, Metallic, for Alternating Cur¬ 
rents .174 

Conduit Conductors.175 

Conductors for Conduits.175 

Conductors, Edison.178-182 

Connection of Underground and Aerial 

Systems.195-197 

Constant of Galvanometer.206 

Condensers.214-217 

Condensers, Arrangement of . . 215-217 

Condenser, Measurement of Galvanom¬ 
eter Resistance by. 238-239 

Condenser, Measurement Battery Re¬ 
sistance by.240 

Conductors.268 

Conductors, Continuous Current . 268-310 

Continuous Current Conductors . 268-310 

Conducting Circuit, Distribution of Po¬ 
tential in.27C-231 

Conductance.281 

Conductance, Graphical Method of De¬ 
termining .281 

Conductors, Heating of.287 

Conductors, Radiation and Convection 

from. 288-290 

Convection. 288-290 

Conductors, Heating of.293 

Concentric Cables, Heating of ... 310 
Conduit Cables, Heating of .... 308 
Conductors for Alternating Currents 

311-371 


Conductors, Alternating.312 

Conductors for Alternating Current, 

Skin Effect in.312 

Constant Current Circuits with Genera¬ 
tors and Receivers at Fixed Distances, 373 
Conditions, Economical, in Series Cir¬ 
cuits . 376-377 

Conductors, Equation for Cost of . 383-385 

Conduits, Equation for Cost of . . . 384 
Conductor Tables for Series Circuits 388-389 


ART. PAGE. 

521 Constant Current Circuits Embracing 
Generators and Receivers at Varying 

Distances. 401 

531 Conical Conductors.411-412 

535-537 Conductors, Cylindrical, Parallel Feed¬ 
ing . 414-416 

538-539 Conical Conductors, Parallel Feeding, 

416-418 

540-541 Conductors, Cylindrical, Anti-Parallel, 

418-420 


542-543 Conical Conductors, Anti-Parallel Feed¬ 
ing . 420-421 

579 Conductors, Efficiency of ... 446-447 

620 Conductors, Buried, Table of Heating 

Limits. 472-475 

629 Conductors, Aerial and Paneled, Heat 

Limits for. 471-475 

663 Conductors, Economy in, With Trans¬ 
former Service.501 

675 Connection, Polyphase System, Meth¬ 
ods of . 511-513 

694 Continuous Current, Long Distance 

Transmission with.524 

695 Construction Line, Long Distance 

Transmission for.525 

697 Conducting Material for Tran'smission 

Systems, Relative Amounts . . 52C-527 

698 Conductors, Cost. 528-554 

700 Conduit, Cost. 533-534 

706 Consumption Coal per Watt Hour, 541-542 

711 Consumption of Gas by Gas Engines . 544 

718-738 Considerations, Commercial, of Trans¬ 
mission Problems. 550-565 

145 Cooking, Insurance Regulations for . . 134 


11 Copper Wire. 8 

11 Copper Resistance, Variations in . . . 9 

11 Copper Wire, Impurities in.9 

12 Copper Wire, Table of the Properties 

of.11 

12 Copper Wire, Fall of Potential in . . 12 


18 C opper Wire, Specifications for . . 26-27 

13-18 Copper Wire, Resistance of . . . 11-30 

20 Copper Wire, Tensions in . . . . 34-35 

144 Cord Pendants, Insurance Regulations 

for.134 

497 Cost of Laying One Additional Ton of 

Copper, Table of. 390-391 

503 Cost of Plant Minimum to obtain Maxi¬ 
mum Income, Design for . . . 393-394 

698-738 Cost of Production and Distribution, 


528-567 

698 Cost, Conductors. 528-534 

700 Cost, Conduit. 533-534 

701 Cost of Telephone and Telegraph 

Lines. 535-537 

702 Cost of Railway Lines .... 537-538 

704 Cost, Power Stations.540 

705 Cost of Producing Energy . . . 540-542 


705 Cost of Installing and Maintaining 

Steam Plants .... 540-541, 556-559 











































INDEX. 


573 


PAGE. 

Cost of Water-Power .542-544 


710-712 Cost of Gas Engines. 544 


712 

Cost of Producing Energy per Kilo- 


Watt Hour .... 

546-550 

713 

Cost of Lighting by Wind-Power . 

545-546 

714 

Cost, Actual, of Producing Electrical 


Energy .... 

547-549 

714 

Cost of Producing Electricity in 

Eu- 


rope. 

547-549 

716 

Cost of Producing Electricity 

in 


America. 

550-552 

727- 

-738 Cost of Line, Tabular Calculation for, 



560-567 

26 

Cross-Arms. 


57 

Cross-Arms. 


60 

Cross-Arm Braces .... 


61 

Cross-Arm Bolts. 


69 

Cross-Arms, Placing of ... . 


69 

Cross-Arms, Location of . . . . 


101 

Cross-Overs and Switches . . . 

. . 112 

174 

Crompton System, The .... 

152-154 

300 

Crosses, Localization of ... . 


33 

Crushing Strength, Timber . . . 


96 

Curves, Railway. 

105-106 

96 

Curves, Location of. 

105-106 

96 

Curve Construction, Right and Left 

. . 106 

244 

Current Unit. 


283-288 Current Strength, Measurement of, 

244-246 

283 

Current Strength by Ammeter 

. . 244 

285 

Current Strength, Measurement of, by 


Voltmeter ........ 


286 

Current Strength, Estimation of, 

by 


Differential Galvanometer . . 

. . 246 

287 

Current Strength, Estimation of, 

by 


Slide Wire Bridge. 



309 Current Measurement of Alternating 

Circuits.257 


313 Currents, Diphase, Measurements on . 259 

329-379 Current, Continuous, Conductors for, 

2G8-310 

351-356 Current Distribution in Branch Circuits 

282-286 

365 Current, Strength to Heat Wires . . . 293 

365 Curves, Current Strength to Heat Wires 

293 

368 Currents in Paneled Wire.295 

383 Current Density in Alternating Current 

Circuits.312 

464 Current, Constant, Circuits with Gener¬ 

ators and Receivers at Fixed Dis¬ 
tances .373 

466 Current Density, Main Circuit 374-376 

544-548 Curves and Tabular Data for Various 
Forms of Conductors, Parallel Sys- 



tern. 

. . . . 421-423 

633 

Curves, Station Load . 

. 476-478 

633 

Curves, Load, St. James Station . 476-478 

635 

Current, Mean Annual, Determination 
of . . ..481 

694 

Current, Continuous, 
Transmission with . 

Long Distance 


akt. page. 

Ill Cut-outs, Automatic.120 

127, 129, 139 Cut-outs, Insurance Regulation for, 

128, 129, 136 

535-537 Cylindrical Conductors, Parallel Feed¬ 
ing . 414-416 

540-541 Cylindrical Conductors, Anti-Parallel 



Feeding . 

418-420 

218 

D’Arsonval Galvanometer . . . 

204-205 

44 

Dead-Ending. 


251 

Deflection, Measurement of, Resistance 


by. 

226-228 

266 

Deflection, Equal Resistance Galvano- 


meter by. 

237-238 

272 

Deflection, Resistance Battery by 

. . 240 

385 

Definition of H . 


387 

Definition of B . 


287 

Definition of .. 


466 

Density Current, Main Circuit 

374-376 


488^494 Depreciation Rates. 386-387 

687 Deptford Plant.521 

469-471 Design for Heating Limit . . . 377-379 

472 Design for Mechanical Strength . 379-380 

473—174 Design for Minimum First Cost of 

Line. 380-381 

475 Design for Minimum First Cost of Sta¬ 
tion .381 

477-498 Design for Minimum First Cost of Plant 
and Minimum Cost of Maintenance 

and Operation. 381-389 

498 Design to Secure Total Minimum First 

Cost of Installation. 389-392 

500 Design for Accomplishment of Best Ser¬ 
vice . 391-392 

503 Design for Minimum Cost of Plant to 

Obtain Maximum Income . . 393-394 

516-519 Design for Series Circuits . . . 398-401 

557-560 Designs, Special, for Three-Wire Sys- 



tern. 

430-432 

68 

Details, Construction. 


495 

Determination of Factor K and K' 

. . 387 

635 

Determination of Mean Annual Current, 481 

633 

Diagram, Station Loads .... 

477-479 

638 

Diagrams, Electric Railway Load, 

483-484 

337 

Dielectrics, Resistance of . . . 

. . 273 

460 

Dielectrics, Character of ... . 


254 

Differential Galvanometer, Measure- 


ment of Resistance by ... . 

. . 230 

286 

Differerential Galvanometer, Measure- 


ment Current Strength .... 


37 

Dimensions for Anchor Poles . 

. 53-57 

312 

Diphase Circuits, Measurements on 

. . 257 


1 Distribution in General ...... 1 

1 Distribution Methods.1 

2 Distribution in Series.2 

3 Distribution in Parallel.2 

5 Distribution, Indirect.3 

109 Discriminating Arrester.118 

343-349 Distribution of Potential in Conducting 

Circuit. 276-281 

351-356 Distribution of Potential and Current 

in Branch Circuits. 282-286 


























































574 


INDEX. 


ART. 

397 

406- 409 

407- 108 


461-520 

461 

522-642 

526-547 

534 

574 

620-621 

653 

660 

664-6C7 

670 

678-694 

698-738 

292 

415 

170 

46 

46 

229 

75 

467 

663 

106 

196 

196 

196 

30 

193 


336 

34F 

384 

399-400 

402-405 

427 

459-460 

379 

670 

18 


84-87 

150 


PAGE. 

Discussion of Energy Equation . . . 324 

Discussion of Solution of Energy Equa¬ 
tions for Circuits with Capacity . 332-333 

Discussion of Energy Equation of Cir¬ 
cuits Containing Resistance, Induc¬ 
tance, and Capacity. 333-335 

Distribution, SerLs. 372-401 

Distribution, Series, Origin of ... . 372 

Distribution, Parallel. 402—487 

Distribution, Methods of . . . 406-423 

Distribution of Potential in Parallel 

Circuits.412 

Distributing Mains.443 

Distributing Mains, Calculation of 467^168 
Distribution, High and Low Potential 

from same Station. 494-495 

Distribution Accumulator.499 

Distribution, Methods of, by Trans¬ 
formers . 502-504 

Distribution of Insulated Transformers, 

Efficiency of. 506-507 

Distance, Long, Transmission Plants,516,525 
Distribution and Production, Cost of, 528-567 
Divided Charge for Measuring Capacity, 

249-250 

Division of Vectors.337 

Dorset Conduit, The.147 

Dynamometers, Wire.65 

Dynamometers.65 

Dynamometers, Siemens.214 

Earth, The, as a Railway Return Circuit 82 
Economical Conditions in Series Cir¬ 
cuits . 376-377 

Economy in Conductors with Trans¬ 
former Service.501 

Edison Lightning Arrester.116 

Edison System.178 

Edison Mains.178—182 

Edison Circuits.178-182 

Effect of Temperature.33-34 

Effect on Alternating Current Circuits 
of Metallic Conductors and Cable 

Sheaths.174 

Effect of Temperature on Resistance . 272 

Effect of Leakage.280 

Effect of Inductance. . 315 

Effect of Mutual Inductance . . 326-327 

Effect of Capacity. 329-351 

Effect of Capacity.346 

Effect of Adjacent Bodies on Capacity of 

Circuits. 370-371 

Efficiency of Conductors . . . 446—447 

Efficiency of Distribution of Insulated 

Transformers. 506-507 

Electrical Properties of Wire, Specifica¬ 
tions for.30-31 

Electric Railway Circuits.77 

Electrolytic Action.89-90 

Electric Gas Lighting, Insurance Regu¬ 
lations for.138 


ART. PAGE. 

121-132 Electric Railways, Insurance Regula¬ 
tions for.126-133 

188-193 Electric Railway Conduits . . . 169-174 

212-241 Electrical Instruments .... 198-223 

228 Electrostatic Voltmeter.213 

241-328 Electrical Measurement, Methods 

of. 223-267 

242 Electrical Inductance.223 

243 Electrical Quantity. 223-224 

277-281 Electro-Mo.ive Force, Measurement 

of. 242-243 

281 Electro-Motive Force, Measurement 

of by Wheatstone Method .... 243 
288-292 Electrostatic Capacity, Measurement 

of. 246-250 

290 Electrostatic Capacity by Thomson’s 

Method.248 

291 Electrostatic Capacity by Gott’s 

Method.249 

292 Electrostatic Capacity by Divided 

Charge, Measurement of . . . 249-250 

317 Electrical Railway Testing.259 

371 Electric Heating. 297-298 

371 Electric Heating, Cost of . . . 297-298 

389 Electro-Motive Force due to Varying 

Field.318 

418 Electro-Motive Forces, Composition and 

Resolution of.3C8-339 

419 Electrical Properties of Simple Circuits 

with One Resistance and One Induct¬ 
ance in Series. 340-341 

425 Electrical Properties, Simple Circuits 

with Several Resistances and Induct¬ 
ances in Series. 344-346 

426 Electrical Properties of Simple Circuits 

with One Resistance and One Capacity 

. in Series,. 346-348 

428 Electro-Motive Force in Simple Circuits 

Containing Resistance and Capacity in 
Series, Graphical Solution of . . . 347 

430 Electrical Properties of Simple Circuits 

with Several Resistances and Capaci¬ 
ties in Series.349 

431 Electrical Properties of Simple Circuits 

Containing Resistance, Inductance, 
and Capacity in Series . . . 349-350 

432 Electrical Properties of Simple Circuits 

with Several Resistances, Inductances, 
and Capacities in Series . . . 350-351 

433 Electrical Properties of Circuits with 

Resistances, Inductances, and Capaci¬ 
ties in Multiple Arc .... 351-354 

638 Electric Railway Load Diagrams . 483-484 

638-642 Electric Railway Wiring .... 483-487 

714 Electrical Energy, Actual Cost of Pro¬ 
ducing . 547-549 

714 Electricity in Europe, Cost of Produc¬ 
ing . 547-549 

714 Electricity in America, Cost of Produc¬ 
ing . 551-552 











































INDEX. 


575 


PAGE. 

Energy Equation.318 

Energy, Expenditure of, in Alternating 

Circuits.. 

Energy Equation, Discussion of . . .324 

405- 407 Energy Equation for Circuits with Ca¬ 

pacity, Solution of. 331-333 

406- 409 Energy Equation for Circuits with Ca¬ 

pacity, Discussion of ... . 332-333 

407- 408 Energy Equation of Circuits containing 

Resistance, Inductance, and Capacity, 


Discussion of. 333-335 

407-408 Energy Equation of Circuits cotanining 
Resistance, Inductance, and Ca¬ 
pacity . 333-335 

705 Energy, Cost of producing . . . 540-542 

712 Energy, Cost of producing per Kilo- 

Watt Hour. 546-550 

710-712 Engines, Gas, Cost of.554 


711 Engines, Gas, Consumption of gas in . 544 

91 Equations for the Catenary.32 

275 Equal Deflection, Measurement of Bat¬ 
tery Resistance.241 

390 Equation of Energy.318 

397 Equation, Energy, Discussion of . . . 324 

400 Equation of Energy, General, for Mutual 

Inductive Circuits.326 

480 Equation for Cost of Conductors . 383-385 

483 Equation for Cost of Conduits .... 384 

434-435 Equivalent Resistance and Inductance, 

Method of. 353-357 

560 European Multiple Wire Systems . . 432 

714 Europe, Cost of Producing Electricity 

in. 547-549 

522-525 Evolution of the Parallel System . 402—106 

85 Examples of Electrolytic Action . . 89-97 

77 Experiments upon the Resistance of 

Return Circuits.84 

107 Expansion Arrester, Air.116 

158 Exterior Wires, Insurance Regulations, 137 

619 Example of Street Loading . . . 466-467 

391 Expenditure of Energy in Alternating 

Circuits.319 

703 Expense Operating Street Railway 538-539 

495 Factor K and K Determination of . 387 

12 Fall of Potential in Copper Wire ... 12 

347 Fall of Potential, Representation of, 278-279 

590-594 Fall of Pressure and Necessary Section 

in Feeders. 453-455 


690 

Falls, Niagara, Plant. 

521 

84 

Farnham’s, I. H., Experiments on Elec- 


trolytic Action. 

. 87-88 

197 

Farranti, Circuits, The .... 

182-183 

197 

Farranti Mains. 

182-183 

293-301 

Faults, Localization of ... • 

250-254 

293-301 

Faults in Line. 

250-254 

297 

Faults, Line, Loop Test for . . 

. . 252 

297 

Faults, Line, Murray’s Method for 

. . 252 

298 

Faults, Line, Varley Method for . 

. . 253 

93 

Feed Wire Insulators and Pole Tops, 97-99 

533 

Feeding, Anti-Parallel .... 

. . 412 


ART. 

390 

391 

397 


art. page. 

535-537 Feeding, Parallel, Conical Conductors 

416-418 

538-539 Feeding, Parallel, Conical Conductors 

416-418 

540-541 Feeding, Anti-Parallel, Cylindrical Con¬ 
ductors . 418-420 

542-543 Feeding, Anti-Parallel, Conical Con¬ 
ductors . 420-421 

563-567 Feeder and Main System . . . 435-439 

573 Feeders, Location of Center of Distri¬ 
bution .443 

576-578 Feeders, Calculation of . ... 444-446 

578 Feeds, Best Number of.446 

590-594 Feeders, Necessary in Section and Fall 

of Pressure. 453-455 

623 Feeds, Calculation of.469 

668 Feeder and Main System with Trans¬ 
former .504 

207 Felten-Guilleaume Cable, Telephone 


191-192 

384 Field, Magnetic, Due to Current . . . 315 

221 Figure of Merit of Galvanometer . . 206 

17 Fire, Inspection of.24-25 

115-162 Fire Underwriters, Regulations . 125-140 

473-474 First Cost of Line, Design for Minimum 

380-381 

58 Fittings, Iron and Steel.74 

559 Five-Wire Systems.432 

130 Fixture Work, Insurance Regulations 

for.131 

16 Flexible Wire, Insulated .... 18-21 

16 Flexible Cable.18-10 

16 Flexible Cable, Tables of . . . 23, 19-21 

43 Fluid Insulators.62 

683 Folspm Plant.519 

389 Force, Electro-Motive, Due to Varying 

Field.318 

206 Fowler-Waring Telephone Cable . 190-191 

685 Frankfort-Lauffen Plant.519 

684 Fresno Plant.520 

139 Fuses, Insurance Regulations for . . 136 

372-375 Fuses . 299-306 

373 Fuse Wire, Length and Carrying Ca¬ 

pacity .303 

374 Fuse Wires, Lead and Tin.305 

14 Galvanizing.13, 16, 31 

14 Galvanized Wire.13-16 

59 Galvanizing of Iron Fittings .... 74 

217-226 Galvanometer. 203-204 

217 Galvanometer, Thomson.203 

218 Galvanometer, D’Arsonval . . . 204-205 

219 Galvanometer, Ballistic .... 205-206 

220 Galvanometer, Constant.206 

221 Galvanometer, Figure of Merit of . . 206 

225 Galvanometer Shunts. 208-209 

266 Galvanometer Resistance, by Equal De¬ 

flection .237 

267 Galvanometer Resistance . . . 237-238 

267-268 Galvanometer Resistance by Wheat¬ 
stone Bridge.238 















































57G 


index ; 


ART. PAGE. 

269 Galvanometer Resistance by Condenser 

238-239 

271 Galvanometer Resistance, Measurement 

by Deflection.240 

187 Gas.168-169 

710-712 Gas Engines, Cost of.554 

711 Gas Consumed by Gas Engines . . . 544 

9 Gauges, Wire.6-25 

9 Gauges, Wire, Relation between ... 7 

17 Gauge, Micrometer.25 

116 Generator or Motor, Insurance Regula¬ 
tions for.126 

400 General Equation of Energy for Mutu¬ 
ally Inductive Circuits.326 

464 Generators and Receivers at Fixed Dis¬ 

tances, Constant Current Circuits . . 373 
521 Generators and Receivers at Varying 

Distances, Constant Current Circuits, 

embracing.401 

613-630 General Design for Conducting System 

in Multiple Arc. 463-472 

370 German Silver Wire for Rheostats . . 299 

205 Glover Cables, Telephone . . . 189-190 

329 Good Conductor.268 

291 Gott’s Method for Electrostatic Ca¬ 
pacity .249 

347 Graphical Representation of Fall of Po¬ 
tential in Conducting Circuit . 278-279 

350 Graphical Method for Determining Con¬ 
ductance .281 

410 Graphical Methods.335 

428 Graphical Solution of Electro-Motive 

Force in Simple Circuits Containing 


Resistance and Capacity in Series . . 347 

74 Ground Wire Construction.80 

236-238 Ground Indicators.219-221 

236-238 Ground Indicators for Alternating Cur¬ 
rent . 220-221 

263-266 Ground Resistance, Measurement of 

236-237 

340 Gutta-Percha, Resistance of .... 274 

36 Guying.45-46 

56 Guy Stubs, Anchor.73 

64 Guy Rods.75 

67 Guy Rope.75 

8 Hard Drawing.4 

392-393 Harmonic Motion. 320-322 

385 H, Definition of.316 

129 Heating, Insurance Regulations for . . 130 

211 Heads for Cables.197 

357 Heating of Conductors.287 

358 Heating of Bare Wires Freely Sus¬ 

pended .288 

365 Heating Power of Current.293 

365 Heating of Conductors.293 

369 Heating of Insulated Wire.295 

370 Heaters.296 

375-379 Heating of Insulated Cables . . 306-310 

378 Heating of Aerial Cables.309 

379 Heating of Concentric Cables .... 310 


ART. PAGE. 

469-471 Heating Limit, Design .... 377-379 

620 Heating Limits, Table of, Buried Con¬ 
ductors . 472, 474-475 

629 Heat Limits for Aerial or Paneled Con¬ 
ductors . 471-472, 475 

25 Height of Poles.38 

686 Heilbronn-Lauffen Plant.519 

685 Helena Plant.520 

608 Hermann Beaded Cable, The, Tele¬ 
phone . 192-193 

131 High Potential Wires, Insurance Regu¬ 
lations for.132 

104 High Resistance Arresters.114 

258-262 High Resistance, Measurement of, 232-235 
653 High and Low Potential Distribution 


from Same Station. 494-495 

404 Hours of Lighting, Table of .... 395 
504 Hours, Service, Table of ..... 395 

615 Hours, Lamp, Number.464 

51 Humming of Wires.69-70 

5 Indirect Distribution.3 

236-238 Indicators, Ground. 220-221 

236-238 Indicators, Ground for Alternating Cur¬ 
rent . 220-221 

242 Inductance, Electrical.223 

302-307 Inductance, Measurement of . . 254-256 

326 Inductance of Aerial Lines.265 

382 Inductance.312 

384 Inductance.315 

324 Inductance, Variable.344 

384 Inductance, Effect of.315 

397-398 Inductance and Resistance, Circuits 

Containing. 324-325 

399-400 Inductance, Mutual, Effect of . . 326-327 

401 Inductance, Coefficients of . . . 327-329 

434-435 Inductance and Resistance Equivalent, 

Method of. 353-357 

450-459 Inductance, Resistance, and Capacity, 

Circuits Containing. 365-371 

180 Inflexible Conduits.160 

224 Inferred Zero.207 

421 Impedance.342 

440 Impedance Tables.360 

440-449 Impedance Tables for Circuits Contain- 

taining Resistance and Inductance, 360-365 

11 Impurities in Copper Wire.9 

686 Indian Orchard Plant.520 

1 Introduction.1 

185 Introduction of Circuits, The . . 167-168 

14 Insulated Wire.17 

16 Insulated Wire, Table of Weights of 19-21 

14 Insulator, Bamboo as an.17 

17 Inspection.24-25 

40 Insulators.58-60 

41-42 Insulators, The Value of .... 60-61 
41-42 Insulators and Insulating, Power of 60-61 

43 Insulators, Fluid.62 

43 Insulators, Oil.62 

63 Insulators.75 

93 Insulators for Feed Wire .... 97-99 



























































INDEX . 


Insulators, Trolley.98-104 

97 Insulators, Strain. 107 


99 Insulators, Railway Section .... 109 

115-162 Insurance Regulations for Circuits, 125-140 
116 Insurance Regulations for Generator or 

Motor . . ..125 

119 Insurance Regulations for Care and At¬ 
tendance . 120 

124 Insurance Regulations for Conductors . 127 

118 Insurance Regulations for Switchboards, 125 

145 Insurance Regulations for Resistance 

Boxes. 137 

148 Insurance Regulations for Lightning Ar¬ 
resters . 137 

119 Insurance Regulations for testing . . 126 

130 Insurance Regulations for Arc Circuit 

Conductors.132 

126 Insurance Regulations for Interior Con¬ 

duits .134 

127 Insurance Regulations for Arc Lamps . 128 

128 Insurance Regulations for Low Pressure 

Circuits.130 

128 Insurance Regulations for Outside Aerial 

Conductors.127 

129 Insurance Regulations for Underground 

Conductors.128 

130 Inside Wiring, Insurance Regulations for, 127 

131 Insurance Regulations for Sizes of Con¬ 

ductors . 128-139 

135 Insurance Regulations for Interior Con¬ 

duit . 131-134 

136 Insurance Regulations for Cut-Outs, 128-129 

137 Insurance Regulations for Fuses . . . 136 

138 Insurance Regulations for Switches . . 129 

139 Insurance Regulations for motors . . 126 

140 Insurance Regulations for Alternating 

Current Sys'.ems. 127-132-137 

140 Insurance Regulations for Arcs on Con¬ 

stant Potential Circuits.132 

141 Insurance Regulations for Fixture Work, 131 

142 Insurance Regulations for Electric Gas 

Lighting ..138 

143 Insurance Regulations for Pendants . . 132 

143 Insurance Regulations for Sockets . . 131 

144 Insurance Regulations for Cord Pendants, 132 

145 Insurance Regulations for Heating . . 130 

145 Insurance Regulations for Cooking . . 130 

131 Insurance Regulations for Electric Rail¬ 
ways .... 133 

121 Insurance Regulations for Power Sta¬ 

tions .126 

124 Insurance Regulations for Trolley Wires, 127 

131 Insurance Regulations for Car-wiring . 133 

115 Insurance Regulations for Lighting and 

Power Wires.125 

122 Insurance Regulations for Batteries . . 123 

126-154 Insurance Regulations for Capacity of 

Wire.128-139 

124 Insurance Regulations for Joints of 

Wires.1-7 


ART. 


PAGE. 

124 

Insurance Regulations for 

Exterior 


Wires. 


124 

Insurance Regulations for Wires Enter- 


ing Buildings . . . . 

. . . .127 

131 

Insurance Regulations for High Poten- 


tial Wires. 


124 

Insurance Regulations for 

Outside 


Wires. 


125 

Insurance Regulations for Inside Wires, 133 

200 

Insulation, Paper .... 


212-241 

Instruments, Electrical . . 

. . 198-223 

226 

Instruments, Weston, The . 

. . 209-211 

258-261 

Insulation Resistances, Measurement 


of. 


261 

Insulation Resistance . . 

. . 234-235 

342 

Insulators, Resistance of 

. ... 275 

369 

Insulated Wires, Heating of 

.... 295 

369 

Insulated Wire Freely Suspended, Heat- 


ing of. 


375-379* 

Insulated Cables, Heating of 

. . 306-310 


498 Installation, Design to Secure Total 

Minimum First Cost of . . . 389-392 

625-629 Inside Wiring, Calculation of . . 470-471 

670 Insulated Transformers, Efficiency of 

Drstribution of. 506-507 

705 Installing and Maintaining Steam Plants, 

Cost of. 540-541, 556-559 

8 Iron and Steel Wire, Properties of . 5 

8-18 Iron and Steel Wire, Strength of . . 5-31 
18 Iron Wire Specifications, British Post- 

Office .28 

18 Iron Wire Specifications.30 

18 Iron Wire, Mechanical Properties of . 31 

20 Iron and Copper Wire, Line Tensions 

in ..34-35 

37 Iron Anchor Poles.47 

37 Iron Top PMes.48-75 

58 Iron and Steel Fittings.74 

59 Iron Fittings, Galvanizing of .... 74 

91 Iron Poles.93-96 

168 Iron Pipe Conduit in Asphalt Concrete, 145 

370 Iron Wire Rheostats, Safe Current for . 297 

85 Jackson, D. C., Experiments on Electro¬ 
lytic Action. 88 

47-49 Joints in Wire. 66-68 

49 Joints, Strength of.67-68 

124 Joints of Wires, Insurance Regulations 

for.127 

176 Johnstone Conduit, The .... 156-157 

209-210 Joints and Splices for Cables . . 193-195 

184 Junction Boxes for Street Railway 

Feeds.166 

357 Joule’s Law.287 

177 Kennedy Conduit.157 

234 Keys.218 

228 Kelvin Voltmeter.213 

249 Kirschhoff’s Laws. 225-226 

37 Lattice Top Poles.48-57 

91 Lattice Pole, Railway.94 

249 Laws, Kirschhoff’s.225 



















































578 


INDEX. 


ART. 


PAGE. 

ART. 


PAGE. 

248 



701 

Lines, Telephone and Telegraph, Cost of, 

342 

Leakage, Line . 

274-276 



535-537 

348 

Leakage, Effect of. 


654 

Leonard System of Motor Regulation . 4.5 

374 

Lead and Ti l Fuse Wire .... 


638 

Load, Electric Railway, Diagrams, 

483-484 

192 

Lenox Avenue Railway Conduit . 

173-174 

637 

Lamps, Arc, on Constant Potential 

66 

Lightning Rods. 



Circuits. 

. . 482 

102-113 

Lightning Arresters. 

113-123 

633 

Loads, Station, Diagrams . . . 

477-479 

112 

Lightning Arresters for Cables 

. . 122 

633 

Load Curves, St. James Station . 

476-478 

113 

Lightning Arresters for Switchboards . 123 

633 

Load, Station, Curves .... 

476-478 

116 

Light, Heat, or Power Circuits, Insur- 

633-636 Loads, Station. 

476-482 


ance Regulations for .... 

. . 125 

629 

Limits, Heat, for Aerial and Paneled 

122 

Lightning Arresters, Insurance Regula- 


Conductors. 471-472, 475 


lations for. 

. . 126 

620 

Limits, Table of Heating, Buried 

Con- 

115 

Lighting and Power Wires, Insurance 


ductors. 

472-475 


Regulations for. 


504 

Loads, Calculation of. 

. . 394 

20 

Line Tension for Iron and Copper Wire, 

619 

Loading, Street, Example of . . 

466-467 



34-35 

617-620 

Loads, Street . 

464-467 

21 

Line Construction . 


465 

Location of Station . 

. . 374 

22 

Lines, Aerial . 

» • 30 

573 

Location of Feeders and Center of Dis- 

29 

Lines, Stresses in. 

. 40-41 


tribution . 


58 

Line Fittings . 


568-572 

Location, Central Station . . . 

439-442 

96 

Line Work, Railway. 

. . 101 

527 

Loop System. 

408-410 

99 

Line Sections, Railway .... 

. . 10.) 

528 

Loop, Spiral . 

. . 410 

101 

Line Crossings, Railway .... 

. . Ill 

678, 694 

Long Distance Transmission Plants 

, 516, 525 

263-264 

Line Resistance, Measurement of, 

236-237 

980 

Long Distance Circuit, Typical . 

. . 517 

293-301 

Line Faults, Localisation of . . 

250-254 

694 

Long Distance Transmission with 

Con- 

296 

Line Faults by Overlap Method . 

. . 251 


tinuous Current . 


300 

Line Crosses, Localization of . . 

. . 253 

695 

Long Distance Transmission Line, 

Con- 

342 

Line Leakage . 

274-276 


struction for . 


96 

Location of Curves . 

105-106 

17 

Machines, Testing . 

. 24-25 

96 

Location of Railway Curve Guy Poles . 106 

676 

Machines, Polyphase. 

513-515 

293-301 

Localization of Faults. 

250-254 

105 

Magnetic Blow-out Arrester . . 

. . 115 

300 

Localization of Crosses .... 


73-74 

Methods of Rail Bonding . . . 

. 80-82 

45 

Loops . 


235 

Magneto. 


297 

Loop Test for Line Faults . . . 

. . 252 

384 

Magnetic Field Conduit and Current . 315 

261 

Loss of Charge, Resistance, Measure- 

384 

Magnetic Field Due to Current . 

. . 315 


ment by . 

. . 234 

196 

Mains, Edison . 

178-182 

191 

Love Railway Conduit .... 

172-173 

197 

Mains, Farranti . 

182-183 

687 

Lowell Plant . 


466 

Main Circuit, Current Density . . 

374-376 

130 

Low Pressure Circuits, Insurance Regu- 

563-567 

Main and Feeder System . . . 

435-439 


lations for . 


574 

Mains, Distributing . 


282 

Lumsden’s Method, Measurement of 

620-621 

Mains, Distributing, Calculation of, 467-468 


E.M.F . 

. . 244 

668 

Main and Feeder System, with Trans- 

282 

Lumsden’s Method, Measurement of 


formers . 



Potential. 

. . 244 

7 

Manufacture, Wire . . . ... 

• • 4 

514 

Lamp Cut-outs. 


182 

Manholes. 

163-165 

614 

Lamps, Ratio of Number Installed to 

335 

Matthieson’s Standard .... 

. . 271 


Number Actually Lighted . . 

. . 464 

166 

McDonald, The, Conduit . . . 

. . 143 

615 

Lamp Hours, Number . - . . 

. . 464 

48 

Mclntire Splices. 

. 66-67 

666 

Lamps, Arc, Transformers for . . 

. . 503 

49 

Mclntire Joints, Strength of . . 

. . 68 

404 

Lighting, Table of Hours of . . 

. . 395 

635 

Mean Annual Current, Determination of, 481 

469-471 

Limit, Heating, Design .... 

377-379 

661 

Means of Accumulators, Regulation by, 

473-474 

Line, Design for Minimum First Cost of, 



499-500 



380-381 

251-277 

Measurement of Resistance . . 

226-242 

695 

Line Construction for Long Distance 

251 

Measurement of Resistance by Deflec- 


Transmission. 

. . 525 


tion. 

226-228 

727-738 

Line, Cost of, Tabular Calculations for, 

254 

Measurement of Resistance by Wheat- 



560-567 


stone Bridge. 

228-229 

713 

Lighting by Wind Power, Cost of, 

545-546 

254 

Measurement of Resistance by Differ- 

702 

Lines, Railway, Cost of ... . 

537-538 


ential Galvanometer . . . . 






















































INDEX. 


579 


ART ’ PAGE. 

235 Measurement of Resistance by Volt¬ 
meter .230 

257 Measurement of Small Resistance, 231-232 
256 Measurement of Resistance by Voltme¬ 
ter and Ammeter. 230-231 

258-262 Measurement of High Resistance . 232-235 
258-259 Measurement of Resistance by Volt¬ 
meter . 232-234 

261 Measurement, Resistance by, Loss of 

Charge.234 

263-264 Measurement of Line Resistance . 236-237 

264 Measurement, Ground Resistance . . 237 

267 Measurement of Battery Resistance by 

Voltmeter.239 

270 Measurement of Battery Resistance . . 239 

274 Measurement of Battery Resistance by 

Condenser.240 

275 Measurement of Battery Resistance by 

Equal Deflection.241 

277-281 Measurement of Potential . . . 242-244 

277-281 Measurement of Electro-Motive Force, 

242-243 

278 Measurement of Potential by Weston 

Voltmeter.242 

280 Measurement, Electro-Motive Force . 243 

282 Measurement of Potential by Lums- 

den’s Method.244 

283-288 Measurement, Current Strength . 244-246 

283 Measurement, Current Strength of Am¬ 

meter .245 

286 Measurement, Current Strength, Differ¬ 
ential Galvanometer Method . . . 246 

288-292 Measurement, Electrostatic Capacity, 

246-250 

304 Measurement of Self-Inductance . . . 255 

304 Measurement of Inductance by means 

of Alternating Currents.255 

306-307 Measurement, Mutual Inductance, 255-256 

307 Measurement of Mutual inductance, 

Coefficients of.256 

308-316 Measurements on Alternating Current 

Circuits. 257-259 

308 Measurement of Alternating Current 

Potential.257 

309 Measurement of Current in Alternating 

Circuits.257 

310 Measurement of Power in Alternating 

Circuits, The. 257-258 

310 Measurement of Power in Alternating 

Current Circuit, Two Voltmeters . .258 

311 Measurement of Power in Alternating 

Current Circuits by three Ammeters . 258 
312-316 Measurements on Polyphase Current 

Circuits.257 

312 Measurements on Diphase Circuits . . 257 

321-325 Measurement of Aerial Line Capacity ,263-265 
326 Measurement of Inductance, Aerial 

Lines.265 

328 Measurement, Mutual Inductance on 

Transmission Lines . . ..... 26( 


ART. 

18 

18 

106 

472 

630 

1 

24 

108 

193 

241-328 

410 

434-435 

526-547 

580-581 

630 

664-667 

4 

675 

17 

473-474 

475 

477-498 

503 

643-697 

4 

688 

120 

392-393 

561 

044-653 

652 

654 

548-561 

554-560 

560 

562 

310-030 

297 

300-307 

328 

399-400 

400 

414 

433 


PAGE. 

Mechanical Properties of Wire ... 29 

Mechanical Properties, Iron Wire . . 31 

Mechanical Magnet Arrester . . . 116 

Mechanical Strength, Design for 379-380 

Mechanical Methods. 471-475 

Methods of Distribution.1 

Methods of Preserving Poles .... 37 
Metal Arresters, Non-arcing .... 117 
Metallic Conduit and Cable Sheaths for 

Alterating Currents .174 

Methods of Electrical Measurement, 223-267 

Methods, Graphical.335 

Methods of Equivalent Resistance and 

Inductance. 353-357 

Methods of Distribution .... 400-423 

Methods of Regulation .... 447-^453 

Methods, Mechanical. 471-475 

Methods of Distribution by Trans¬ 
formers . 502-504 

Methods of Connection, Polyphase 

System.511-513 

Micrometer Gauge.25 

Minimum First Cost of Line, Design 

for . 380-381 

Minimum First Cost of Station, Design 

for.381 

Minimum First Cost of Plant and Mini¬ 
mum Cost of Maintenance and Opera¬ 
tion, Design for. 381-389 

Minimum Cost of Plant to obtain Maxi¬ 
mum Income, Design for . . . 393-394 

Miscellaneous Methods .... 488-527 

Mixed Systems.2 

Montmorency Falls Plant.521 

Motors, Insurance Regulations for . . 126 

Motion, Harmonic. 320-322 

Motor Transformers.434 

Motor Transformers. 488-495 

Motor Transformers, Running and Feed¬ 
ing in Series. 493-494 

Motor Regulation, Leonard System of . 495 
Multiple Wire Systems .... 423^434 

Multiple Series Systems, Modifications 
of Three-Wire System .... 428-432 

Multiple Wire Systems, European . . 432 

Multiple Wire Systems, Relative Areas 

covered by.435 

Multiple Arc, General Design for Con¬ 
ducting System in. 463-472 

Murray’s Method for Line Faults . . 252 

Mutual Inductance, Measurement of, 255-256 
Mutual Inductance on Transmission 

Lines.267 

Mutual Inductance, Effect of . . 326-327 

Mutually Inductive Circuits, General 

Equation of Energy for.326 

Multiplication of Vectors.337 

Multiple Arc, Circuits containing Re¬ 
sistances, Inductances, and Capacities 
in. 351-354 




































INDEX. 


580 


ART. 

43G 

455 

689 

690 
108 
109 

614 

615 

691 
43 

215 

254 

248 

332 

703 

461 

124 

124 

296 

12 

12 

366 

368 

629 

167 

200 

201 

3 

179 

459-460 

522-642 

522-525 

535-537 

538-539 

544-548 


204 

351-356 


130 


62 

91 

168-169 

26 

69 

477-498 


PAGE. 

Mutual Inductance, Properties of Cir¬ 
cuits containing. 357-360 

Multipliers to Transform E. S. C. G. S. 
Units into E.M.F., Table of . . . 368 

Nevada Co. Plant.521 

Niagara Falls Plant.521 

Non-arcing Metal Arresters . . . .117 

Non-arcing Wurtz Continuous Current 

Arrester.119 

■Number of Lamps Installed to Lamps 
Actually Lighted, Ratio of ... . 464 

Number Lamp Hours.464 

Ogden Plant.522 

Oil Insulators.62 

Ohm-meter. 202-203 

Ohm-meter, Measurement of Resistance, 230 

Ohm’s Law.225 

Ohm's Law.269 

Operating Expense Street Railway, 538-539 
Origin of Series Distribution .... 372 
Outside Aerial Conductors, Insurance 

Regulations for.127 

Outside Wires, Insurance Regulations for, 127 
Overlap Method for Line Faults . . . 251 

Paneled Wire.12 

Paneled Wire, Carrying Capacity of . . 12 

Paneled Wire, Safe Current for . . . 294 

Paneled Wires, Current in.295 

Paneled and Aerial Conductors, Heat 

Limits for. 471-475 

Paper Conduit.144 

Paper Insulation.185 

Paper Cables.186 

Parallel, Distribution in.2 

Parisian Conduits ..159 

Parallel Wires, Capacity of Circuits 

Modified by. 370-371 

Parallel Distribution. 402-487 

Parallel System, Evolution of . . 402-406 

Parallel Feeding, Cylindrical Conduc¬ 
tors . 414-416 

Parallel Feeding, Conical Conductors, 

416-418 

Parallel System, Curves and Tabular 
Data for Various Forms of Conductors, 

421-423 

Patterson Cable, Telephone . . 188-189 

Potential Distribution in Branch Cir¬ 
cuits . 282-286 

Pendants and Sockets, Insurance Regu¬ 
lations for.132 

Pins.39 

Pins.74-75 

Pipe Poles.94-96 

Pipe Conduits.144-147 

Placing of Cross-Arms.38-39 

Placing of Cross-Arms.76 

Plant, Design for Minium First Cost 
of and Minium Cost of Maintenance 
and Operation. 381-389 


ART. PAGE. 

678-694 Plants,Transmission, Long Distance, 516-525 

681 Plant, Big Cotton Wood.519 

682 Plant, Blue Lakes.519 

683 Plant, Folsom.519 

684 Plant, Fresno.520 

685 Plant, Helena.520 

686 Plant, Indian Orchard.520 

687 Plant, Lowell.521 

688 Plant, Montmorency Falls.521 

689 Plant, Nevada Co.521 

690 Plant, Niagara.521 

691 Plant, Ogden.522 

692 Plant, Portland.523 

693 Plant, St. Anthony’s Falls.523 

186 Pneumatic Rodding.167 

23 Poles.36-37 

23 Poles, Wooden.36-37 

24 Poles, Methods of Preservation . . 37-38 

25 Poles, Height of.. . . 38 

28 Pole Tops.40 

33-35 Pole Strengths, Calculations for . . 41-45 

36 Poles, Methods of Guying .... 45-46 

37 Poles, Anchor.47-57 

37 Poles with Iron Tops.4S-57 

38 Pole Setting.58 

53-71 Pole Line Specifications.72-76 

55 Poles.73 

86-92 Poles, Railway.90-97 

91 Poles, Iron.93-95 

91 Pole, Center, Construction.96 

93 Pole Tops, Feed Wire Insulators . 97-99 
93 Pole Tops.97-99 

312-316 Polyphase Current Circuits, Measure¬ 
ments on.257 

673-677 Polyphase Transmission .... 508-516 

675 Polyphase System, Methods of Connec¬ 

tion . 511-513 

676 Polyphase Machines.513-515 

638 Pomona Plant, The . 521 

213 Portable Testing Sets.200 

592 Portland Plant.523 

277-281 Potential, Measurement of . . . 242-244 

308 Potential in Alternating Current Cir¬ 
cuits, Measurements of.257 

343-349 Potential in Conducting Circuit . 276-281 


351-356 Potential and Current, Distribution of 

in Branch Circuits. 282-286 

534 Potential in Parallel Circuits, Distribu¬ 
tion of.412 

653 Potential, High and Low, Distribution 

from Same Station. 494-495 

53 Power Circuits.72-76 

121 Power Stations, Insurance, Regulations 

for.126 

200 Power Circuits.185-186 

247 Power, Unit of.224 

310 Power in Alternating Current Circuits, 

Measurement ol. 257-258 

310 Power, Measurement in Alternating 

Current Circuits by Two Voltmeters . 258 




































































INDEX. 


581 


ART. 

311 

704 

707 

713 

590-594 

124 

6 

8 

13 

12 

16 

18 

419 


425 


PAGE. 

Power, Measurement in Alternating 
Current Circuits by Three Ammeters, 258 
Power Stations, Cost ... ... 540 

Power, Water, Cost of .... 542-544 

Power, Wind, Cost of Lighting by, 545-546 
Pressure, Fall of, and Necessary Sec¬ 
tion in Feeders . 453-455 

Primary Conductors, Insurance Regu¬ 
lations for .127 

. 4 

. 5 

12-16 
. 11 


426 


430 


431 


432 


433 

436 

698-738 

705 

712 

718-738 

411 

360-363 

360-368 

72 

73-85 

73-74 

74 

74 

75-77 

75 

77 

78 

79 


Properties of Wire. 

Properties of Iron and Steel Wire 
Properties of Silicon Bronze Wire 
Properties of Copper Wire . . . 

Properties of Flexible Cables . . 23, 19-21 
Properties of Iron Wire, Mechanical . 31 
Properties, Electrical, of Simple Cir¬ 
cuits with One Resistance and One 
Inductance in Series .... 340-341 

Properties, Electrical, Simple Circuits 
with Several Resistances and Induc¬ 
tances in Series. 344-346 

Properties, Electrical, of Simple Cir¬ 
cuits with One Resistance and One 

Capacity in Series. 346-348 

Properties, Electrical, of Simple Cir¬ 
cuits with Several Resistances and 

Capacities, in Series.349 

Properties, Electrical, of Simple Cir¬ 
cuits Containing Resistance, Induc¬ 
tance, and Capacity in Series . 349-350 

Properties, Electrical, of Simple Cir¬ 
cuits with Several Resistances, In¬ 
ductances, and Capacities in Series, 

.A) < 1 

Properties, Electrical, of Circuits with 
Resistances, Inductances, and Capa¬ 
cities in Multiple Arc . . . 351-354 

Properties of Circuits Containing Mu¬ 
tual Inductance. 357-360 

Production and Distributing, Cost of, 

528-567 

Producing Energy, Cost of . . 540-542 

Producing Energy, Cost of, per Kilo- 

Watt Houi*. 546-550 

Problems, Transmission, Commercial, 

Considerations of. 550-565 

Quantities, Vector .335 

Radiation and Convection from Con¬ 
ductors . 288-290 

Radiation . 288-290 

Railway Circuits.77 

Railway Return Circuit . . . 

Rail Bonding, Methods of . . 

Rail Bonding . 

Railway Return Wire . . 

Rails as Railway Return Circin . 

Railway Return Circuit, the Eat h as a, 82 
Rail Circuit, Resistance of . . . . 84 

Rail Welding.84 

Railway Joints, Cast Connection of . 85 


77-90 
80-82 
80-82 
. 80 
82-84 


ART. 

81 

86-92 

88 

89-90 

91 

91 

96 

96 

96 

96 

96 

98 

99 
99 

100 

101 

586 

638-642 

642 

702 

703 
89 

488-494 

614 

420 

416 

464 

223 

689 

505-515 

580-581 

654 

661 

9 

373 

562 

697 

11 

13-18 

76-77 

118 

246 

251-277 

251 

254 

254 

257 

258-259 

258-261 


PAGE. 

Railway Bonds, Size of ...... 86 

Railway Poles.90-97 

Railway Construction, Center Pole . 91 

Railway Span Wire Construction . 92-93 

Railway Lattice Pole .94 

. 95-96 
, . 101 
10-106 
. . 105 
If) -106 
106 


Railway Iron Pipe Poles 
Railway Line Work . . . 

Railway Curves .... 

Railway Turn-outs .... 

Railway Curves. 

Railway Curve Guy Poles, Location of 
Railway Line Anchors . . 

Railway Section Insulators 
Railway Line Sections . . 

Railway Lines, Switches for 
Railway Line Crossings . . 

Railway Work, Compensator in 
Railway Electric Wiring 
Railway Systems, Three-Wire 
Railway Lines, Cost of . . 


1CC- 


108 
109 

109 

110 
. . Ill 
. . 452 
483-4S7 
. . 487 
537-538 


Railway, Street, Operating Expense, 538-539 

Ratchets, Span Wire.92 

Rates of Depreciation .... 386-387 

Ratio of Number of Lamps Installed 
to Lamps Actually Lighted .... 464 

Reactance.341 

Reciprocal of Vectors. 337 

Receivers and Generators at Fixed Dis¬ 
tances, Constant Current Circuits . . 373 

Reduction to Zero.207 

Redlands Plant, The.522 

Regulation. 394-398 

Regulation, Methods of ... . 447-453 

Regulation, Motor, Leonard’s System of, 495 
Regulation by Means of Accumulators, 

499-500 

Relations between Wire Gauges, Table of, 7 
Relation between Carrying Capacity and 

Length of Fuse Wires.303 

Relative Areas covered by Multiple 

Wire Systems.435 

Relative Amounts of Conducting Mate¬ 
rial for Transmission Systems . 526-527 

Resistance of Silicon Bronze Wire . 12-16 

Resistance of Copper Wire .... 11-30 

Resistance of Rail Bonding .... 83-84 
Resistance Boxes, Insurance Regula¬ 
tions for.126 

Resistance.224 

Resistance, Measurement of . . 226-242 

Resistance, Measurement of, by Deflec¬ 
tion . 226-228 

Resistance, Measurement by Wheat¬ 
stone Bridge. 228 229 

Resistance, Measurement by Ohm-meter, 230 
Resistance, Small, Measurement of, 231-232 
Resistance, Measurement of, by Volt¬ 
meter . 232-234 

Resistance, Insulation, Measurement 
of. 234-235 









































582 


JNDEX . 


ART. 

261 

205-276 

206 

266 

267-268 


PAGE. 

Resistance, Loss of Charge by, Measure¬ 
ment .234 

Resistance, Special Methods for . 237-242 

Resistance, Galvanometer, by Equal 

Deflection.. . . 237 

Resistance, Galvanometer . . . 237-238 

Resistance, Galvanometer, by Wheat- 



stone Bridge. 

238 

195 

Siemens Cable . . . 


272 

Resistance, Battery, by Deflection . . 

240 

229 

Siemens Dynamometer 

.214 

332 

Resistance. 

269 

11 

Silicon Bronze Wire . 

. 12-16 

331 

Resistance, Specific. 

269 

11 

Silicon Bronze Wire, Table of Proper- 

334 

Resistance, Table for Metals . . . . 

270 


ties of. 

. 12-16 

335 

Resistance, Table for Unit Lengths . . 

271 

419 

Simple Circuits with 

One Resistance 

336 

Resistance, Variation with Temperature, 

272 


and One Inductance 

in Series, Elec- 

337 

Resistance of Dielectrics. 

273 


trical Properties of . 

.... 340-341 

340 

Resistance of Gutta-Percha .... 


425 

Simple Circuits with 

Several Resist- 

397-398 

Resistance and Inductance, Circuits 



ances and Inductances in Series, Elec- 


418 

422 

429 


Containing. 324-325 

407-46S Resistance, Inductance, and Capacity, 
Circuits Containing, Equation of 

E lcrgy. 333-335 

Resolution and Composi.ion of Electro- 

Motive Forces . 338-339 

Resistances, Variable. 342-343 

Resistance, Variable, in Circuits Con¬ 
taining Resistance and Capacity, 348-349 
434-435 Resistance and Inductance, Equivalent, 

Method of. 353-357 

450-459 Resistance, Inductance, and Capacity, 

Circuits Containing . . . . , 365-371 

Rheostats.296 

Rheostats and Heaters.296 

Right and Left Curve Construction . . 106 

Riveted Railway Joints.85 

Rods, Guy.75 

Rods, Lightning.75 

Rodding.167 

Rolling of Wire.5 

Rope, Guy.75 

Running Board.63-64 

Safe Current for Paneled Wire ... 12 

Safe Current for Paneled Wire, Table of, 294 
Safe Current for Iron Wire, Rheostats . 297 
Safe Current for German Silver Wire, 

Rheostats.299 

Sags and Tensions for Erecting Iron and 

Copper Wire.34 

Sand Barrels.58 

Secondary Circuit Wiring, Transformers, 505 
Self-Inductance, Measurement of . . 255 

Series, Distribution in.2 

Series Distribution. 372-401 

Series Distribution, Origin of . . . . 372 

Series Circuits, Classification of . 372-374 

Series Circuits, Economical Conditions 

in. 376-377 

Series Circuits, Conductor Tables, 388-389 
Service, Design for Accomplishment for 

Best . .. 392-393 

Service Hours, Table of.395 


370 

370 

96 

79 

64 

66 

186 

S 

67 

46 

12 

366 

370 

370 

19 

39 

668 

304 

2 

461-520 

461 

463 

467 

497 

500 

504 


ART. 

516-519 

554-560 

663 

38 

225 


PAGE. 

Series Circuits, Design for . . . 398-401 

Series Systems, Multiple and Modifica¬ 
tion of Three-Wire System . . 428-432 

Service Transformer, Economy in Con¬ 
ductors .501 

Setting Poles.58 

Shunts for Galvanometer . . . 208-209 


426 

428 

429 

430 

431 

432 

126-154 

373 

382 

383 
214 
287 

114 

130 

405- 407 

406- 409 
248 


trical Properties of. 344-346 

Simple Circuits with One Resistance 
and One Capacity in Series, Electri¬ 
cal Properties of. 346-348 

Simple Circuits Containing Resistance 
and Capacity in Series, Graphical So¬ 
lution of Electro-Motive Force . . 347 

Simple Circuits Containing Resistance 
and Capacity,Variable Capacity in, 348-349 
Simple Circuits with Several Resistances 
and Capacities i.i Series, Electrical 

Properties of.349 

Simple Circuits Containing Resistance, 
Inductance, and Capacity in Series, 
Electrical Properties of . . . 349-350 

Simple Circuits with Several Resist¬ 
ances, Inductances and Capacies, Elec¬ 
trical Properties of. 350-351 

Sizes of Conductors, Insurance Regula¬ 
tions for.128-139 

Size, Fuse Wires, Table of.300 

Skin Effect, Alternating Currents . . . 312 

Skin Effect.312 

Slide Wire Bridge. 201-202 

Slide Wire Bridge, Method for Estimat¬ 
ing Current Strength.246 

Sneak Current Arresters.124 

Sockets, Insurance Regulations for . . 131 

Solution of Energy, Equations for Cir¬ 
cuits with capacity. 331-333 

Solution of Energy, Equations for Cir¬ 
cuits with capacity, Discussion of 332-333 
Solution, Graphical, of Electro-Motive 
Force in Simple Circuits Containing 



Resistance and Capacity in Series . 

. 347 

89-90 

Span Wire Railway, Construction 

92-93 

89 

Span Wire, Construction .... 

91-93 

89 

Span Wire Ratchets. 

. 92 

90 

Span Wire. 


18 

Specification for Iron Wire . . . 

. 28 

18 

Specification for Copper Wire 

26-27 

18 

Specifications, British Post-Office 

26-27 

18 

Specifications, British Wire . . . 

26-27 














































INDEX. 


583 


528 

47-49 

48 

209-210 

693 

335 

465 

475 

568-574 

6)3-636 

633 

633 

633 

659 

672 

704 
8 

91 

178 

633 

8-18 

705 

16 

29 

33 

46 

49 
49 

49 
97 

184 

472 

617-620 

619 

703 

187 

199 

199 

413 

659 

672 

50 
378 
100 
113 


tern. 

Spiral Loop. 

Splices, Wire. 

Splices, Mclntire. 

Splices for Cables. 

St. Anthony’s Falls Plant . . 

Standard of Copper Resistance 

Station Location. 

Station, Design for Minimum, 

Cost of. 

Station, Central Location . . 

Station Loads. 

Station Load Curves .... 

Station Load Curves, St. James 
Station Loads, Diagram . . 

Station, Sub-Accumulation . . 

Station, Sub-Transformers as . 

Stations, Power, Cost . . . 

Steel Wire, Properties of . . 

Steel Poles. 

St. James Conduit. 

St. James Station, Load Curves 
Strength of Iron and Steel Wire 
Steam Plants, Cost of Installii 
Maintaining .... 540-6 

Stranded Cables, Table of . 

Stresses in Lines. 

Strength, Timber. 

Stringing of Wires .... 

Strength of Joints. 

Strength of Western Union Joints 
Strength of Mclntire Joints 

Strain Insulators. 

Street Railway Junction Boxes 
Strength, Mechanical, Design for 

Street Loads. 

Street Loading, Example of . 

Street Railway, Operating Expense, 538-539 
Subway, Gas in ... . 

Submarine Cables . . . 

Sub-aqueous Cables . . 

Subtraction of Vectors . 

Sub-Station Accumulators 
Sub-Stations, Transformers as 
Suspension of Aerial Cables 
Suspended Cables, Heating of 
Switches for Railway Lines 
Switchboard Protectors . . 


ART. 


PAGE. 

ART. 


PAGE. 

18 

Specifications, American Wire 

. 28-31 

118 

Switchboards, Insurance Regulations 

18 

Specifications for Electrical Properties 


for. 



of Wire. 


127 

Switches, Insurance Regulations for 

. 129 

18 

Specifications for Copper Wire 

. 29-31 

4 

Systems, Mixed. 

2 

18 

Specifications, Iron Wire . . . 

. . 30 

522-525 System, Parallel, Evolution of 

402-406 

54-71 

Specification for Pole Line . . . 

. 73-76 

527 

System, Loop. 

408-410 

332 

Specific Resistance. 


529 

System, Tree ....... 

. . 410 

342 

Specific Resistance . 

. . 269 

530 

System, Closet. 

410-411 

342 

Specific Resistance of Insulators . 

. . 274 

548-554 System, Three-Wire. 

423-428 

239-240 Speed Recorder, Boyer’s . . . 

221-222 

548-561 

Systems, Multiple Wire .... 

423-424 

265-276 

Special Methods for Resistance . 

237-342 

555 

System, Three-Wire, with One Genera- 

557-560 Special Designs for Three-Wire 

Sys- 


tor. 



430-432 

559 


560 

. 66-68 

563- 

. 66-67 

642 

193-195 

646 

. . 523 

654 

. . 271 

675 

. . 374 


'irst 

668 



439-442 

9 

476-482 

12 

476-478 

16 

476-478 

334 

477-479 

335 

498-499 

364 

507-508 


. . 540 

383 

. . 5 


. . 94 

383 



476-478 

504 

. 5-31 

440 

and 

440- 

556-559 


. 20-23 

455 

. 40-41 



497 

. 63-64 



497 

. . 68 


. . 68 

504 

. . 107 

544- 

. . 166 


379-580 


464-467 

620 

466-467 


538-539 

727- 

168-169 

52 

183-185 

198 

183-185 

202- 

. . 337 

203 

498-499 

204 

507-508 

691 

. 68-69 

701 

. . 309 


109-110 

20 

. . 123 



Systems, Five-Wire.432 

Systems, Multiple Wire, European . . 432 

System, Feeder and Main . . . 435-439 

Systems, Railway, Three-Wire . . . 487 

System, Three-Wire, Compensator on . 490 
System, Leonard, Motor Regulation . 495 
System, Polyphase, Methods of Connec¬ 
tion . 511-513 

System, Feeder and Main, Transform¬ 


ers with.504 

Table of Wire Gauges.7 

Table of Properties of Copper Wire . . 11 

Table, Combination Wire.24 

Table of Resistance of Metals .... 270 
Table of Resistance for Unit Lengths . 271 
Table of Variation of Copper Resistance 

with Temperature.291 

Table of Thickness of Shells in Alterna¬ 
ting Current Conductors.314 

Table of Virtual Resistance in Alterna¬ 
ting Current Circuits.315 

Table of Hours of Lighting.395 

Tables, Impedance.360 

Tables, Impedance for Circuits Contain¬ 
ing Resistance and Inductance . . 360-65 

Table of Multipliers to Transform E. S. 

C. G. S. Units into E.M.F .368 

Tables, Conductor, for Series Circuits, 

388-389 

Table of Cost of Laying One Additional 

Ton of Copper. 390-391 

Table of Service Hours.395 

Tabular Data and Curves for Various 
Forms of Conductors, Parallel System 

421-423 

Table of Heating Limits, Buried Con¬ 
ductors . 472—175 

Tabular Calculation for Cost of Line 560-567 
Telephone Lines, Transposition of . 70-72 

Telegraph Cables.183 

Telephone Cables.188-194 

Telephone Cable, British Post-Office . 188 
Telephone Cable, Patterson . . 188-189 

Telluride Plant.522 

Telephone and Telegraph Lines, Cost of, 

535-537 

Temperature, Influence on Aeriai Lines, 

33-34 















































584 


INDEX. 


ART. PAGE. 

336 Temperature, Effect on Resistance . . 272 

341 Temperature in Dielectrics, Resistance 

of.274 

17 Tension Testing-Machines .... 22-25 

19 Tension Aerial Lines., . .31 

19 Tension and Sags for Erecting Iron and 

Copper Wire.34 

33 Tensile Strength, Timber.43 

172-174 Terra Cotta Conduit.148-152 


173 Terra-Cotta Separate Duct Conduit,The, 150 


17 Testing.24 

17 Testing of Wire.24-25 

17 Testing-Machines.24-25 

123 Testing, Insurance Regulations for . . 127 

213 Testing Sets.200 

213 Testing Sets, Portable.200 

517 Testing of Electrical Railways.... 259 

105 Thomson-Houston Arrester .... 115 

217 Thomson Galvanometer.203 

232 Thomson-Houston Wattmeter .... 217 

290 Thomson Method for Electrostatic Ca¬ 
pacity .248 


554 Three-Wire System with One Generator, 430 

548-554 Three-Wire System. 423-128 

554-560 Three-Wire System, Multiple Series, 

Systems and Modification of . 428-432 

557-560 Three-Wire System, Special Designs for 

430-432 

642 Three-Wire Railway Systems .... 487 

646 Three-Wire System, Compensator on . 490 


33 Timber, Strength of.43 

514 Time Cut-outs.398 

14 Tinning.15-16 

14 Tinned Wire. 13-16 

374 Tin and Lead Fuse Wire.305 

681 Tivoli Station.518 


17 Torsion Testing-Machines.25 

498 Total Minimum First Cost of Installa¬ 
tion, Design to Secure .... 389-392 

52 Transposition of Telephone Lines . 70-72 

201 Transmission Cable.186-188 

328 Transmission Lines, Measurement, Mu¬ 
tual Inductance.267 

14 Tree Wire.17 

313 Triphase Circuits, Measurements on . 259 

561 Transformers, Motor.434 

644-653 Transformers, Motor. 488-495 

632 Transformers, Motor, Running and 

Feeding in Series. 493-494 

662-673 Transformers. 500-508 

663 Transformer Service with Economy in 

Conductors.501 

664-667 Transformers by Methods of Distribu¬ 
tion . 502-504 

666 Transformers for Arc Lamps .... 503 

668 Transformers with Main System, Feeder 

and.504 

668 Transformers, Secondary Circuit Wiring, 505 

C70 Transformers, Insulated, Efficiency of 

Distribution of . . ’. . . . 506-537 


ART. PAGE. 

672 Transformers as Sub-Stations . . 507-508 

673-677 Transmission, Polyphase . . . 508-516 

678-694 Transmission Plants, Long Distance, 516-525 
694 Transmission, Continuous Current, Long 


Distance with.524 

695 Transmission, Long Distance Line, Con¬ 
struction for.525 


697 Transmission Systems, Relative 

Amounts of Conducting Material, 526-527 
718-738 Transmission Problems, Commercial 

Considerations of. 550-565 

529 Tree System.410 

47 Trolley Wire Splices.66 

95 Trolley Insulators.98-104 

124 Trolley Wires, Insurance Regulations for, 

127 

96 Turn-Outs, Railway.105 

44 Tying and Dead-Ending.62-63 

44 Tying.62-63 

70 Tying of Wires.76 

680 Typical Long Distance Circuit.... 527 

387 fJL, Definition of.317 

127 Underground Conductors, Insurance 

Regulations for ..128 

163 Underground Circuits, Construction of . 141 

211 Underground and Aerial Systems, Con¬ 
nection of.195-197 

244 Unit of Current.224 

247 Unit of Power.224 

335 Unit Lengths, Table, Resistance of . . 271 

455 Units, E. S. C. G. S., into E.M.F. 

Table, to Transform.368 

41-42 Value of Insulators, The.60-61 

165 Valentine, The, Conduit.142 

395-396 Values, Average, of Circuit Constants, 

322-324 


11 

Variations in Copper Resistance . 

. . 9 

26 

Variations of Temperature, Influence of, 



33-34 

298 

Varley Method for Line Faults 

. . 253 

324 

Variable Inductances. 


336 

Variation of Resistance with Tempera- 


ture. 


341 

Variation of Dielectrics with Tempera- 


ture. 


389 

Varying Field, Fdectro-Motive 

Force 


Due to. 


422 

Variable Resistances. 

342-343 

429 

Variable Capacity in Simple Circuits 


Containing Resistance and Capacity, 



348-349 

429 

Variable Resistance in Circuits 

Con- 


tabling Resistance and Capacity, 

348-349 

411 

Vector Quantities. 


412 

Vectors, Addition of. 

. . 337 

413 

Vectors, Subtraction of ... . 

. . 337 

414 

Vectors, Multiplication of . . . 

. . 337 

415 

Vectors, Division of. 


416 

Vectors, Reciprocal of . . . . 


226 

Voltmeter, Weston. 

209-211 






















































INDEX. 


585 


ART * PAGE. 

227 Voltmeter, Cardew. 211 

228 Voltmeter, Electrostatic.213 

228 Voltmeter, Kelvin.213 

256 Voltmeter and Ammeter, Resistance, 

Measurement by. 230-231 

258-259 Voltmeter, Measurement of Resistance 

by. 232-234 

285 Voltmeter, Measurement for Current 

Strength.245 

232 Wattmeters.217 

232 Wattmeter, Thomson-Houston . . . 217 

247 Watt.224 

706 Watt Hour, Coal Consumption per, 541-542 

707 Water-Power, Cost of .... 542-544 

16 Weights per Mile of Insulated Wire . 19-21 

78 Welding of Rails.84 

49 Western Union Joints, Strength of . . 68 

107 Westinghouse Arrester.116 

226 Weston Instruments. 209-211 

213 Wheatstone Bridge. 198-201 

254 Wheatstone Bridge, Resistance Meas¬ 
urement by . 228-229 

267-268 Wheatstone Bridge, Galvanometer Re¬ 
sistance by.238 

281 Wheatstone’s Method of Electro-Mo¬ 
tive Force Measurement.243 

713 Wind-Power, Cost of Lighting by, 545-546 

6 Wire, Properties of.4 

7 Wire Manufacture.4 

8 Wire, Rolling of.5 

9 Wire Gauges.6-25 

11 Wire, Silicon Bronze.13-16 

11 Wire, Copper, Impurities in ... k 9 

13 Wire Composite.10 

14 Wire, Galvanized.13-16 

14 Wire, Tinned.13-16 

14 Wire, Tinned and Galvanized . . . 13-16 

14 Wire, Insulated.17 

14 Wire, Tree.77 

17 Wire, Testing of.24-25 


ART. 


PAGE. 


18 

Wire, Iron, Specifications for . . . 

. 28 

18 

Wire, Mechanical Properties of . . 

. 29 

20 

Wire, Iron and Copper, Line Tension, 34-35 

46 

Wires, stringing of. 

63-64 

46 

Wire Dynamometers.. 


47-49 

Wire Joints. 

66-68 

47 

Wire Splices, Trolley. 

. 66 

47-49 

Wire Splices. 

66-68 

51 

Wires, Humming of. 

69-70 

71 

Wire Joint. 

. 76 

74 

Wire, Railway Return. 

. 80 

125 

Wiring, Inside, Insurance Regulations 

for, 


127 


124 


Wires Entering Buildings, Insurance 

Regulations for.127 

125 Wire, Inside, Insurance Regulations for, 127 
358 Wires, Bare, Freely Suspended, Heat¬ 
ing of.289 

360-363 Wires, Radiation and Convection from, 

288-290 

372-375 Wires, Fuse. 299-306 

358 Wires, Bare, Freely Suspended, Heat¬ 
ing of.288 

548-561 Wire, Multiple, System .... 423-424 

625-629 Wiring, Inside, Calculation of . . 470-471 

638-642 Wiring, Electric Railway . . . 483-487 

668 Wiring, Secondary Circuit Transformer, 505 

23 Wooden Poles.36-37 

86-87 Wooden Poles, Railway.90-91 

168 Wrought-Iron Pipe Conduit .... 144 
168 Wrought-Iron Pipe in Asphaltic Cement, 145 
104 Wurtz Arrester.114 

108 Wurtz Non-Arcing Arrester . . . .117 

109 Wurtz Non-Arcing Continuous Current 

Arrester.119 

166 Wyckoff, The, Conduit.143 

168 Zinc Tubing in Hydraulic Cement . . 145 

182 Zurich Conduit.162 

224 Zero, Inferred.207 

223 Zero, Reduction to.207 





































































































. 














































































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of Stability in the Well-Proportioned Arch. 8vo, half morocco..$4.00 

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Catalogue of the Van Nostrand 

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No. i. CHIMNEYS FOR FURNACES AND STEAM-BOILERS. 

By R. Armstrong, C.E. Third American edition, revised and partly 
rewritten, with an appendix on Theory of Chimney Draught, by F. E. 
Idell, M.E. 

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edition, revised by Prof. R. H. Thurston. 

No. 3. PRACTICAL DESIGNING OF RETAINING-WALLS. 

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No. 4. PROPORTIONS OF PINS USED IN BRIDGES. Second 
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No. 5. VENTILATION OF BUILDINGS. By W. F. Butler. Second 

edition, re-edited and enlarged by James L. Greenleaf, C.E. 

No. 6. ON THE DESIGNING AND CONSTRUCTION OF 

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No. 7. SURCHARGED AND DIFFERENT FORMS OF RE- 

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No. 8. A TREATISE ON THE COMPOUND ENGINE. By John 

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No. 9. A TREATISE ON FUEL. By Arthur V. Abbott, C. E. 

Founded on the original treatise of C. William Siemens, D.C.L. 

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Richard H. Buel, C.E. 

No. 11. THEORY OF ARCHES. By Prof. W. Allan. 

No. 12. A THEORY OF VOUSSOIR ARCHES. By Prof. W. E. 
Cain. Second edition, revised and enlarged. Illustrated. 

No. 13. GASES MET WITH IN COAL-MINES. By J. J. Atkinson. 

Third edition, icvised and enlarged by Edward H Williams, jun. 












D. VAN NOSTRAND COMPANY'S 


No. 14 . FRICTION OF AIR IN MINES. By J. J. Atkinson. 

No. 15 . SKEW ARCHES. By Prof. E. W. Hyde, C.E. Illustrated. 

No. 16 . A GRAPHIC METHOD FOR SOLVING CERTAIN 

ALGEBRAIC EQUATIONS. By Prof. George L Vose. CERTAIN 

No. 17 . WATER AND WATER-SUPPLY. By Prof. W. H. Corfield 

of the University College, London. 

No 'u\t S , EWERAGE AND SEWAGE PURIFICATION. By 

M. N. Baker, Assoc. Kd. Engineering News . 


No. 19. STRENGTH OF BEAMS UNDER TRANSVERSE 

LOADS. By Prof. W. Allan, author of “Theory of Arches.” 

No. 20. BRIDGE AND TUNNEL CENTRES. By John B. Mc- 
Master, C.E. 


No. 21. SAFETY VALVES. By Richard II. Buel, C.E. Second edition. 
No 22. HIGH MASONRY DAMS. By John B. McMaster, C.E. 

No. 23. THE FATIGUE OF METALS UNDER REPEATED 

STRAINS. With Various Tables of Results and Experiments. From 
the German of Prof. Ludwig Spangenburgh, with a Preface bv S. II. 
Shreve, A.M. 


No. 24. A PRACTICAL TREATISE ON THE TEETH OF 

WHEELS. By Prof. S. W. Robinson. Second edition, revised. 

No. 25. ON THE THEORY AND CALCULATION OF CON¬ 
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No. 26. PRACTICAL TREATISE ON THE PROPERTIES OF 

CONTINUOUS BRIDGES. By Charles Bender, C.E. 

No. 27. ON BOILER INCRUSTATION AND CORROSION 

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Idell, M. E. 

No. 28. TRANSMISSION OF POWER BY WIRE ROPES 

By Albert W. Stahl, U.S.N. Second edition. 

No. 29. STEAM INJECTORS. Translated from the French ot 
M. Leon Pochet. 


No. 30. TERRESTRIAL MAGNETISM, AND THE MAGNET¬ 
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IVo. 31. THE SANITARY CONDITION OF DWELLING- 

HOUSES IN TOWN AND COUNTRY. By George E. Waring, jun, 

No. 32. CABLE-MAKING FOR SUSPENSION BRIDGES. By 

W. Hildenbrand, C.E. 

No. 33-_ MECHANICS OF VENTILATION. By George W. Rafter, 
C.E. New edition (1895), revised by author. 

No. 34. FOUNDATIONS. By Prof. Jules Gaudard, C.E. Translated 
from the French. 

No. 35. THE ANEROID BAROMETER : ITS CONSTRUC- 

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No. 36, MATTER AND MOTION. By J. Clerk Maxwell, M.A. 
Second American edition. 




















SCIENCE SERIES. 


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No. 37. GEOGRAPHICAL SURVEYING: ITS USES, METH¬ 
ODS, AND RESULTS. By Frank De Yeaux Carpenter, C.E. 

No. 38. MAXIMUM STRESSES IN FRAMED BRIDGES. By 

Prof. William Cain, A.M., C.E. 

No. 39. A HANDBOOK OF THE ELECTRO-MAGNETIC 

TELEGRAPH. By A E. Loring. 

No. 40. TRANSMISSION OF POWER BY COMPRESSED AIR. 

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No. 41. STRENGTH OF MATERIALS. By William Kent, C.E. 

No. 42. VOUSSOIR ARCHES APPLIED TO STONE BRIDGES, 

TUNNELS, CULVERTS, AND DOMES. By Prof. William Cain. 

No. 43. WAVE AND VORTEX MOTION. By Dr. Thomas Craig of 
Johns Hopkins University. 

No. 44. TURBINE WHEELS. By Prof. W. P. Trowbridge, Columbia 
College. Second edition. 

No. 45. THERMODYNAMICS. By Prof. H. T. Eddy, University of 
Cincinnati. 

No. 46. ICE-MAKING MACHINES. New edition, revised and en¬ 
larged by Prof. J. E. Denton. From the French of M. Le Doux. 

No. 47. LINKAGES; THE DIFFERENT FORMS AND USES 

OF ARTICULATED LINKS. By J. D. C. de Roos. 

No. 48. THEORY OF SOLID AND BRACED ARCHES. By 

William Cain, C.E. 

No. 49 ON THE MOTION OF A SOLID IN A FLUID. By 

Thomas Craig, Ph.D. 

No. 50. DWELLING-HOUSES: THEIR SANITARY CON¬ 
STRUCTION AND ARRANGEMENTS. By Prof. W. Ii. Corfield. 

No. 51. THE TELESCOPE : ITS CONSTRUCTION, ETC. By 

Thomas Nolan. 

No. 52. IMAGINARY QUANTITIES. Translated from the French of 

M. Argand. By Prof. Hardy. 

No. 53. INDUCTION COILS: HOW MADE AND HOW USED. 

Fifth edition. 

No. 54. KINEMATICS OF MACHINERY. By Prof. Kennedy. With 
an introduction by Prof. R. H. Thurston. 

No. <5. SEWER GASES: THEIR NATURE AND ORIGIN. By 

A. de Varona. 

No. 56. THE ACTUAL LATERAL PRESSURE OF EARTH¬ 
WORK. By Benjamin Baker, M. Inst. C.E. 

No. 57. INCANDESCENT ELECTRIC LIGHTING. A Practical 

Description of the Edison System. By L. H. Latimer, to which is 
added the Design and Operation of Incandescent Stations, by C. J. 
Field, and the Maximum Efficiency of Incandescent Lamps, by John 
W. Howell. 

No. 58. THE VENTILATION OF COAL-MINES. By W. Fairley 

M.E , F.S.S. * 






















D. VAN NO STRAND COMPANY'S 


No. 59. RAILROAD ECONOMICS; OR, NOTES, WITH COM¬ 
MENTS. By S. W. Robinson, C.E. 

No. 60. STRENGTH OF WROUGHT-IRON BRIDGE MEM¬ 
BERS. By S. W. Robinson, C.E. 

No. 61. POTABLE WATER AND THE DIFFERENT METH¬ 
ODS OF DETECTING IMPURITIES. By Charles W. Folkard. 

No. 62. THE THEORY OF THE GAS-ENGrNE. By Dugald Clerk. 

Second edition. With additional matter. Edited by F. E. I dell, M.E. 

No. 63. HOUSE DRAINAGE AND SANITARY PLUMBING. 

By W. P. Gerhard. Sixth edition, revised. 

No. 64. ELECTRO-MAGNETS. ByTh.du Moncel. 2d revised edition. 

No. 65. POCKET LOGARITHMS TO FOUR PLACES OF DECI¬ 
MALS. 

No. 66. DYNAMO-ELECTRIC MACHINERY. By S. P. Thompson 
With notes by F. L. Pope. Third edition. 

No. 67. HYDRAULIC TABLES BASED ON “KUTTER’S 

FORMULA.” By P. J. Flynn. 

No. 68. STEAM-HEATING. By Robert Briggs. Second edition, revised, 
with additions by A. R. Wolff. 

No. 69. CHEMICAL PROBLEMS. By Prof. J. C. Foye. Second 
edition, revised and enlarged. 

No. 70. EXPLOSIVES AND EXPLOSIVE COMPOUNDS. By 

M. Bertholet. 

No. 71. DYNAMIC ELECTRICITY. By John Hopkinson, J. A. 
Schoolbred, and R. E. Day. 

No. 72. TOPOGRAPHICAL SURVEYING. By George J. Specht, 
Prof. A. S. Hardy, John B. McMaster, and H. F. Walling. 

No. 73. SYMBOLIC ALGEBRA; OR, THE ALGEBRA OF 

ALGEBRAIC NUMBERS. By Prof. W. Cain. 

No. 74. TESTING MACHINES: THEIR HISTORY, CON¬ 
STRUCTION, AND USE. By Arthur V. Abbott. 

No.--;. RECENT PROGRESS IN DYNAMO-ELECTRIC MA¬ 
CHINES. Being a Supplement to Dynamo-Electric Machinery. By 
Prof. Sylvanus P. Thompson. 

No. 76. MODERN REPRODUCTIVE GRAPHIC PROCESSES. 

By Lieut. James S. Pettit, U.S.A. 

No. 77. STADIA SURVEYING. The Theory ot Stadia Measurements. 
By Arthur Winslow. 

No. 78. THE STEAM-ENGINE INDICATOR, AND ITS USE 

By W. B. Le Van. 

No. 79. THE FIGURE OF THE EARTH. By Frank C. Roberts.C.E. 

No. 80. HEALTHY FOUNDATIONS FOR HOUSES. By Glenr, 
Brown 


V 

















SCIENCE SERIES. 


No. 81 . WATER METERS : COMPARATIVE TESTS OF 

ACCURACY, DELIVERY, ETC. Distinctive features of the Worth¬ 
ington, Kennedy, Siemens, and Hesse meters. By Ross E. Browne. 

No. 82 . THE PRESERVATION OF TIMBER BY THE USE 

OF ANTISEPTICS. By Samuel Bagster Boulton, C.E. 

No. 83. MECHANICAL INTEGRATORS. By Prof. Ilenry S. H. 

Shaw, C.E. 

No. 84. FLOW OF WATER IN OPEN CHANNELS, PIPES, 

CONDUITS, SEWERS, ETC. With Tables. By P. J. Flynn, C.E. 

No. 85. THE LUMINIFEROUS iETHER. By Prof, de Volson Wood. 

No. 86. HAND-BOOK OF MINERALOGY; DETERMINATION 

AND DESCRIPTION OF MINERALS FOUND IN THE UNITED 
STATES. By Prof. J. C. Foye. 

No. 87. TREATISE ON THE THEORY OF THE CON¬ 
STRUCTION OF IIELICOIDAL OBLIQUE ARCHES. By John 
L. Culley, C.E. 

No. 88. BEAMS AND GIRDERS. Practical Formulas for their Re¬ 
sistance. By P. H. Phil brick. 

No. 89. MODERN GUN-COTTON: ITS MANUFACTURE, 

PROPERTIES, AND ANALYSIS. By Lieut. John P. Wisser, U.S.A. 

No. go. ROTARY MOTION, AS APPLIED TO THE GYRO¬ 
SCOPE. By Gen. J. G. Barnard. 

No. 91 . LEVELING: BAROMETRIC, TRIGONOMETRIC, AND 

SPIRIT. By Prof. I. O. Baker. 

No. 92. PETROLEUM : ITS PRODUCTION AND USE. By 

Boverton Redw r ood, F.I.C., F.C.S. 

No. 93 . RECENT PRACTICE IN THE SANITARY DRAIN¬ 
AGE OF BUILDINGS. With Memoranda on the Cost of Plumbing 
Work. Second edition, re vised. By William Paul Gerhard, C. E. 

No. 94. THE TREATMENT OF SEWAGE. By Dr. C. Meymott 
Tidy. 

No. 95 - PLATE GIRDER CONSTRUCTION. By Isami Iliroi, C.E. 
Second edition, revised and enlarged. Plates and Illustrations. 

No. 96. ALTERNATE CURRENT MACHINERY. By Gisbert 
Kapp, Assoc. M. Inst., C.E. 

No. 97 . THE DISPOSAL OF HOUSEHOLD WASTE. By W, 

Paul Gerhard, Sanitary Engineer. 

No. 98 . PRACTICAL DYNAMO-BUILDING FOR AMATEURS. 

HOW TO WIND FOR ANY OUTPUT. By Frederick Walker. 
Fully illustrated. 

No. 99 .® TRIPLE-EXPANSION ENGINES AND ENGINE 
TRIALS. By Prof. Osborne Reynolds. Edited, with notes, etc., by 
F. E. Idell, M. E. 
























Scale of Cost of Boilers, High-Speed and Corliss Engines per Horse-Power m Dollars 


Table No. 74. Sheet A 

Cost of Installing and Maintaining Steam Plant. 

Scale of Horse-Power of Dynamos. 



60 100 150 200 260 300 

Scale of Horse-Power of Corliss and Single Act ing Engines. 


0 


360 


400 


Seale of Cost of Dynamos and Willans Engines per Horse-Power in Dollars. 




















































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































.4348 (2 


Values of 4 log e -|L_ .01 

lo ? '/l -j- (~ )‘f and .4343 (2 log M) _3.8 3.6 

“ “ (2 logrV J9 18 


.02 .03 


3.4 

17 


3.2 

16 


.04 


.05 .06 .07 


3 2.8 

15 14 


2.6 

13 


2.4 

12 


11 


.08 


10 


1.8 1.6 

0 8 


09 .1 

1.4 


Table 44, Sheet 3. Seepages 367 - 371 . 


1.2 


.1 

5 


8 .6 .4 .2 


3 2 1 


(2 log £A 



1 


Values of (2 log Vl -f and .4843 (2 log-££) 4 3.8 3.6 3.4 3.2 3 2.8 2.62.4 2.2 2 1.81.61.41.2 1 .8 .6 .4 .2 


Values of 4 log r j 


.3 


.4 


.5 


4 5 6 

Distance between Wires in Inclies=tl- 


10 














































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































Short 1. 


Table No. 44. s« 


Pages 3G0-364 


Distance between Axes of Wires in Inches =&__ 


000260 



-Values of (0.5 + 2 log's .f) 


40 45 60 55 60 65 

Diameter of Wire in Mils=s2 r- 


100 Mils. 


Values of r 












































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































Table No. 76 


See Page 564 , 




K 7 


r 


Cost of Generating Station per HV 


A 



A 


y 


Cost of Energy at Generating Station per IP. hour. 

















































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































DEC 2 It98 









♦ 




ft 


















Table !Xo. 75. See Pages 560 - 563 . 

-Interest and Depreciation plus Cost of Water plus Cost of Labor or Cost at Generating* Station per IP.- 

65 en !! 'ft c. Jft 9X aft 2K 9ft IS 1ft 


60 


50 


45 


40 


35 


30 


20 


15 


10 


7000 


/ 


6500 


6000 


5500 


5000 


© 


4000 


2 

.5 3500 


+3 

ae 

o 

rj 3000 


2500 


2000 


1500 




1000 


500 


Interest and Depreciation on Line per Mile.- 


100 


350 


300 


200 


175 


150 


125 


100 


75 


\ 50 


150 


200 


250 


350 


400 


450 


500 


550 


600 


650 





£ 































V s 

o 






















_ 

\ 




\ 




























»— 

X 






\ 




























1 






\ 


























>-< 

o 



6? 
































X 




















1 

— 













w 

4\ 

































s 























ST 












X 









\ 










v 

\ 

\ 



















































■M 

** 



































H 

















\ 








































































\ 


























\ 


























\ 












































































































\ 









































'v 




\ 






















z 




10 


15 


35 


CJD 


40 


60 


65 


70 


/ 


20 25 30 35 40 45 50 

——Interest and Depreciation on Generating* Plant per KP- 


60 


75 


Note: 


\ 


550 


500 


750 


1000 


1250 • 

© 

pp 

•pp 

© 

© 

1500 

JS 


S 

1750 O 

s 


a 

2000 ^ 

'd 

& 

2250 $ 
© 

M 

2500 


2750 


3000 


3250 


3500 


/ 


50 


100 


150 


200 


250 300 350 400 450 500 

—Interest and Depreciation on Line per Mile.— 


550 


600 


650 


7*00 


The Interest and Depreciation figures in 
parentheses to be used. in connection with. 
“Cost of Line per.Mile’-' onlyi 

In this table IP maj be replaced by any 
other unit, as Watt, Kilowatt, Board of 
Trade Units,-etc. 

The transverse lines for the length of Line 
in Miles, are used also to find Interest and 
Depreciation on whole line per IP and de¬ 
signate then 1 IP, 3 Hi 3 IP etc. or also 
10 IP, 20 IP, 30 IP etc.-etc. 


















































































































































































































































































































































































































































































































































































































































































































































































































Note: 


Table No. 77. See Pages 565 — 566 . 


For soft copper conductors 
use lines marked S. C. 

For hard copper conductors 
use lines marked H. C. 


Value of FK + K J (t4-d«) 



\ 



+ 


KA 





WW 


J 



Table No. 24. 


















































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































t© 

o* 

© 


Value of Vf, L (FK+K'(i+dJJ ov/ 


& 

o 

c 


C.I 

o 


Table No. 78. See Page 566. 


12500 


11250 


10000 


8750 


Value of L fb (i+<b) +1/ (i+d^)) or B 




H 


















































. 












s 


























1 



4 










\ 















L 







































\ 1 



















\r 












[\ 
























































\ 





\ 






















. i 













\J 













r 

l\ 

































































J 

























> 















\ 












N 






































\ 
























































































\ 

















































































\ 












\ 













*1 

ill 






s 

-i 







© 

© 






© 



































• 























sq 

u;i 

re 

i 

lie 

he 

s. 


































































































































































































_L 



































































! 






































□ 





















































_ 

“T 

i 

— 













































-\ 

- 













































J 

— 










\ 

\ 

~~ 
































i 












\ 

\ 









\ 




















i 

_ 



T 

i 

I— 











\ 


\ 

\ 









\ 








\ 









U 





_ip 







































1 \ 




. 

III 

—lu — 



































_ 








-4— 












































1 




V 




























\ 












-1- 

















\ 























\ 





Hi 













































ill 








































\q\ 





!' 































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-*• 





1 

\ 





l| 


























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<=> 

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ll 
















\ 







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II 



























-- 












1 \ 





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1 

























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* 

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\ 




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hp S 






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Ps 




























1 

-1 

1 

I 

















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V 

ks 

a 












l .. 













1 



















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1 

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1 





















% 





















\ 


JLl 

















\ 





* 































A 



















\ 






\ 









1 










i V 

























\ 








\ 

— 

1 

J 













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1 




















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1 

r I 




















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i 

1 















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NA 













1 

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V '|\| 
















\ 

















\ 







v 1 \ 

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V 1 






































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\ 














\ 

























\ 




















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\| 







\ 



























































\ 






















\ 































' 























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+- 

1 

1 




































\ 






1 


— 








































\ 






| 














































i 

i 

i 
















\ 































( 













































\V 

J 


































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- 

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.. 














\ 

















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\ 



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\ 


j 












































a 

\ 


L 









































V 



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\ 


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\ 

\ 


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i 












































ii— 

1 












































i 


1 

1 
























































V 





























V 





1 








































V 

\ 




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1 







































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1 

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1 

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s 

% 







— 













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w \\ \ P 

\ l 










































\ 1 


1 

[ 1 























































































































































_ 





























































1 










































r 

-L 1 

1—- 






200C0 


15000 - 


© 


X 

loooo c 


d= 

















1 

















































































1 

> 


































































































\ 

















































1 

























lv 






t« 






«c 





J Ci 

X-O 








w< 

i§J 






© 

© 






Cl 

© 





j © 

L J 9 

















aJ 

lu 

e 

OT 

j 

a 

) ( 

lit 

i 

} + 

-b 



















C 










c 

















l« 

r 









T 













JH 



-o 

f-l 


V 

4. 




i 


4 . 

>nal 

a 

'e 
















































J 


































































































































































l 



































































































































































_ 





















































J 

















































































-J 



























L 

























j 

L 


























_ 

_ 

L 


























- 


























J 






& 


+ d/-)) 


or 


Conduct * 


n 


11250 


10000 


5000 


8750 


7500 


0250 


Value of I*p L (FK+K^i-hf.j] or / 




.875 


• 3 l 9 


.625 

-Value of s=V"d~. or cross-sectional area of Conductor in square inches. - 


.125 


'IfUM Wf loo/ J-»*P WMJ 




































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































